diff --git a/abstract_client.cpp b/abstract_client.cpp
--- a/abstract_client.cpp
+++ b/abstract_client.cpp
@@ -297,7 +297,7 @@
                              ? rules()->checkOpacityActive(qRound(opacity() * 100.0))
                              : rules()->checkOpacityInactive(qRound(opacity() * 100.0));
     setOpacity(ruledOpacity / 100.0);
-    workspace()->setActiveClient(act ? this : NULL);
+    workspace()->setActiveClient(act ? this : nullptr);
 
     if (!m_active)
         cancelAutoRaise();
diff --git a/activation.cpp b/activation.cpp
--- a/activation.cpp
+++ b/activation.cpp
@@ -240,12 +240,12 @@
     StackingUpdatesBlocker blocker(this);
     ++set_active_client_recursion;
     updateFocusMousePosition(Cursor::pos());
-    if (active_client != NULL) {
+    if (active_client != nullptr) {
         // note that this may call setActiveClient( NULL ), therefore the recursion counter
         active_client->setActive(false);
     }
     active_client = c;
-    Q_ASSERT(c == NULL || c->isActive());
+    Q_ASSERT(c == nullptr || c->isActive());
 
     if (active_client) {
         last_active_client = active_client;
@@ -292,9 +292,9 @@
  */
 void Workspace::activateClient(AbstractClient* c, bool force)
 {
-    if (c == NULL) {
+    if (c == nullptr) {
         focusToNull();
-        setActiveClient(NULL);
+        setActiveClient(nullptr);
         return;
     }
     raiseClient(c);
@@ -359,7 +359,7 @@
 
     if (flags & ActivityFocus) {
         AbstractClient* modal = c->findModal();
-        if (modal != NULL && modal != c) {
+        if (modal != nullptr && modal != c) {
             if (!modal->isOnDesktop(c->desktop()))
                 modal->setDesktop(c->desktop());
             if (!modal->isShown(true) && !modal->isMinimized())  // forced desktop or utility window
@@ -437,7 +437,7 @@
             return client;
         }
     }
-    return 0;
+    return nullptr;
 }
 
 // deactivates 'c' and activates next client
@@ -449,9 +449,9 @@
 
     closeActivePopup();
 
-    if (c != NULL) {
+    if (c != nullptr) {
         if (c == active_client)
-            setActiveClient(NULL);
+            setActiveClient(nullptr);
         should_get_focus.removeAll(c);
     }
 
@@ -465,15 +465,15 @@
     if (!options->focusPolicyIsReasonable())
         return false;
 
-    AbstractClient* get_focus = NULL;
+    AbstractClient* get_focus = nullptr;
 
     // precedence on keeping the current tabgroup active. to the user that's the same window
     if (c && c->tabGroup() && c->isShown(false)) {
         if (c == c->tabGroup()->current())
             c->tabGroup()->activateNext();
         get_focus = c->tabGroup()->current();
         if (get_focus == c) // single tab case - should not happen
-            get_focus = NULL;
+            get_focus = nullptr;
     }
 
     const int desktop = VirtualDesktopManager::self()->current();
@@ -485,7 +485,7 @@
         get_focus = clientUnderMouse(c ? c->screen() : screens()->current());
         if (get_focus && (get_focus == c || get_focus->isDesktop())) {
             // should rather not happen, but it cannot get the focus. rest of usability is tested above
-            get_focus = NULL;
+            get_focus = nullptr;
         }
     }
 
@@ -504,10 +504,10 @@
         }
     }
 
-    if (get_focus == NULL)   // last chance: focus the desktop
+    if (get_focus == nullptr)   // last chance: focus the desktop
         get_focus = findDesktop(true, desktop);
 
-    if (get_focus != NULL)
+    if (get_focus != nullptr)
         requestFocus(get_focus);
     else
         focusToNull();
@@ -525,9 +525,9 @@
     closeActivePopup();
     const int desktop = VirtualDesktopManager::self()->current();
     AbstractClient *get_focus = FocusChain::self()->getForActivation(desktop, new_screen);
-    if (get_focus == NULL)
+    if (get_focus == nullptr)
         get_focus = findDesktop(true, desktop);
-    if (get_focus != NULL && get_focus != mostRecentlyActivatedClient())
+    if (get_focus != nullptr && get_focus != mostRecentlyActivatedClient())
         requestFocus(get_focus);
     screens()->setCurrent(new_screen);
 }
@@ -601,7 +601,7 @@
 
     // No active client, it's ok to pass focus
     // NOTICE that extreme protection needs to be handled before to allow protection on unmanged windows
-    if (ac == NULL || ac->isDesktop()) {
+    if (ac == nullptr || ac->isDesktop()) {
         qCDebug(KWIN_CORE) << "Activation: No client active, allowing";
         return true; // no active client -> always allow
     }
@@ -655,7 +655,7 @@
         return true;
     if (level == 4)   // extreme
         return false;
-    if (ac == NULL || ac->isDesktop()) {
+    if (ac == nullptr || ac->isDesktop()) {
         qCDebug(KWIN_CORE) << "Raising: No client active, allowing";
         return true; // no active client -> always allow
     }
@@ -718,7 +718,7 @@
             && (m_userTime == XCB_TIME_CURRENT_TIME
                 || NET::timestampCompare(time, m_userTime) > 0)) {    // time > user_time
         m_userTime = time;
-        shade_below = NULL; // do not hover re-shade a window after it got interaction
+        shade_below = nullptr; // do not hover re-shade a window after it got interaction
     }
     group()->updateUserTime(m_userTime);
 }
@@ -738,7 +738,7 @@
 
     // newer ASN timestamp always replaces user timestamp, unless user timestamp is 0
     // helps e.g. with konqy reusing
-    if (asn_data != NULL && time != 0) {
+    if (asn_data != nullptr && time != 0) {
         if (asn_id->timestamp() != 0
                 && (time == -1U || NET::timestampCompare(asn_id->timestamp(), time) > 0)) {
             time = asn_id->timestamp();
@@ -754,7 +754,7 @@
         // from already running application if this application
         // is not the active one (unless focus stealing prevention is turned off).
         Client* act = dynamic_cast<Client*>(workspace()->mostRecentlyActivatedClient());
-        if (act != NULL && !belongToSameApplication(act, this, SameApplicationCheck::RelaxedForActive)) {
+        if (act != nullptr && !belongToSameApplication(act, this, SameApplicationCheck::RelaxedForActive)) {
             bool first_window = true;
             auto sameApplicationActiveHackPredicate = [this](const Client *cl) {
                 // ignore already existing splashes, toolbars, utilities and menus,
@@ -777,7 +777,7 @@
                     ; // is transient for currently active window, even though it's not
                 // the same app (e.g. kcookiejar dialog) -> allow activation
                 else if (groupTransient() &&
-                        findInList<Client, Client>(clientMainClients(), sameApplicationActiveHackPredicate) == NULL)
+                        findInList<Client, Client>(clientMainClients(), sameApplicationActiveHackPredicate) == nullptr)
                     ; // standalone transient
                 else
                     first_window = false;
@@ -813,7 +813,7 @@
     xcb_timestamp_t time = m_userTime;
     if (time == 0)   // doesn't want focus after showing
         return 0;
-    Q_ASSERT(group() != NULL);
+    Q_ASSERT(group() != nullptr);
     if (time == -1U
             || (group()->userTime() != -1U
                 && NET::timestampCompare(group()->userTime(), time) > 0))
diff --git a/activities.cpp b/activities.cpp
--- a/activities.cpp
+++ b/activities.cpp
@@ -47,7 +47,7 @@
 
 Activities::~Activities()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 KActivities::Consumer::ServiceStatus Activities::serviceStatus() const
diff --git a/client.h b/client.h
--- a/client.h
+++ b/client.h
@@ -101,7 +101,7 @@
     AbstractClient* findModal(bool allow_itself = false) override;
     const Group* group() const override;
     Group* group() override;
-    void checkGroup(Group* gr = NULL, bool force = false);
+    void checkGroup(Group* gr = nullptr, bool force = false);
     void changeClientLeaderGroup(Group* gr);
     void updateWindowRules(Rules::Types selection) override;
     void updateFullscreenMonitors(NETFullscreenMonitors topology);
diff --git a/client.cpp b/client.cpp
--- a/client.cpp
+++ b/client.cpp
@@ -108,17 +108,17 @@
     , m_managed(false)
     , m_transientForId(XCB_WINDOW_NONE)
     , m_originalTransientForId(XCB_WINDOW_NONE)
-    , shade_below(NULL)
+    , shade_below(nullptr)
     , m_motif(atoms->motif_wm_hints)
     , blocks_compositing(false)
-    , shadeHoverTimer(NULL)
+    , shadeHoverTimer(nullptr)
     , m_colormap(XCB_COLORMAP_NONE)
-    , in_group(NULL)
-    , ping_timer(NULL)
+    , in_group(nullptr)
+    , ping_timer(nullptr)
     , m_killHelperPID(0)
     , m_pingTimestamp(XCB_TIME_CURRENT_TIME)
     , m_userTime(XCB_TIME_CURRENT_TIME)   // Not known yet
-    , allowed_actions(0)
+    , allowed_actions(nullptr)
     , shade_geometry_change(false)
     , sm_stacking_order(-1)
     , activitiesDefined(false)
@@ -130,14 +130,14 @@
 {
     // TODO: Do all as initialization
     syncRequest.counter = syncRequest.alarm = XCB_NONE;
-    syncRequest.timeout = syncRequest.failsafeTimeout = NULL;
+    syncRequest.timeout = syncRequest.failsafeTimeout = nullptr;
     syncRequest.lastTimestamp = xTime();
     syncRequest.isPending = false;
 
     // Set the initial mapping state
     mapping_state = Withdrawn;
 
-    info = NULL;
+    info = nullptr;
 
     shade_mode = ShadeNone;
     deleting = false;
@@ -227,7 +227,7 @@
     }
 #endif
     destroyWindowManagementInterface();
-    Deleted* del = NULL;
+    Deleted* del = nullptr;
     if (!on_shutdown) {
         del = Deleted::create(this);
     }
@@ -877,7 +877,7 @@
         if (shade_mode == ShadeHover) {
             ToplevelList order = workspace()->stackingOrder();
             // invalidate, since "this" could be the topmost toplevel and shade_below dangeling
-            shade_below = NULL;
+            shade_below = nullptr;
             // this is likely related to the index parameter?!
             for (int idx = order.indexOf(this) + 1; idx < order.count(); ++idx) {
                 shade_below = qobject_cast<Client*>(order.at(idx));
@@ -888,7 +888,7 @@
             if (shade_below && shade_below->isNormalWindow())
                 workspace()->raiseClient(this);
             else
-                shade_below = NULL;
+                shade_below = nullptr;
         }
         m_wrapper.map();
         m_client.map();
@@ -923,7 +923,7 @@
 void Client::cancelShadeHoverTimer()
 {
     delete shadeHoverTimer;
-    shadeHoverTimer = 0;
+    shadeHoverTimer = nullptr;
 }
 
 void Client::toggleShade()
@@ -1101,7 +1101,7 @@
         workspace()->forceRestacking();
         if (Xcb::Extensions::self()->isShapeInputAvailable()) {
             xcb_shape_rectangles(connection(), XCB_SHAPE_SO_SET, XCB_SHAPE_SK_INPUT,
-                                 XCB_CLIP_ORDERING_UNSORTED, frameId(), 0, 0, 0, NULL);
+                                 XCB_CLIP_ORDERING_UNSORTED, frameId(), 0, 0, 0, nullptr);
         }
     } else {
         workspace()->forceRestacking();
@@ -1179,7 +1179,7 @@
         return; // Can't ping :(
     if (options->killPingTimeout() == 0)
         return; // Turned off
-    if (ping_timer != NULL)
+    if (ping_timer != nullptr)
         return; // Pinging already
     ping_timer = new QTimer(this);
     connect(ping_timer, &QTimer::timeout, this,
@@ -1212,7 +1212,7 @@
     if (NET::timestampCompare(timestamp, m_pingTimestamp) != 0)
         return;
     delete ping_timer;
-    ping_timer = NULL;
+    ping_timer = nullptr;
 
     setUnresponsive(false);
 
@@ -1794,16 +1794,16 @@
     const bool usedToBlock = blocks_compositing;
     blocks_compositing = rules()->checkBlockCompositing(block && options->windowsBlockCompositing());
     if (usedToBlock != blocks_compositing) {
-        emit blockingCompositingChanged(blocks_compositing ? this : 0);
+        emit blockingCompositingChanged(blocks_compositing ? this : nullptr);
     }
 }
 
 void Client::updateAllowedActions(bool force)
 {
     if (!isManaged() && !force)
         return;
     NET::Actions old_allowed_actions = NET::Actions(allowed_actions);
-    allowed_actions = 0;
+    allowed_actions = nullptr;
     if (isMovable())
         allowed_actions |= NET::ActionMove;
     if (isResizable())
diff --git a/client_machine.h b/client_machine.h
--- a/client_machine.h
+++ b/client_machine.h
@@ -34,7 +34,7 @@
 {
     Q_OBJECT
 public:
-    explicit GetAddrInfo(const QByteArray &hostName, QObject *parent = NULL);
+    explicit GetAddrInfo(const QByteArray &hostName, QObject *parent = nullptr);
     ~GetAddrInfo() override;
 
     void resolve();
@@ -64,7 +64,7 @@
 {
     Q_OBJECT
 public:
-    explicit ClientMachine(QObject *parent = NULL);
+    explicit ClientMachine(QObject *parent = nullptr);
     ~ClientMachine() override;
 
     void resolve(xcb_window_t window, xcb_window_t clientLeader);
diff --git a/client_machine.cpp b/client_machine.cpp
--- a/client_machine.cpp
+++ b/client_machine.cpp
@@ -54,8 +54,8 @@
     , m_ownResolved(false)
     , m_hostName(hostName)
     , m_addressHints(new addrinfo)
-    , m_address(NULL)
-    , m_ownAddress(NULL)
+    , m_address(nullptr)
+    , m_ownAddress(nullptr)
     , m_watcher(new QFutureWatcher<int>(this))
     , m_ownAddressWatcher(new QFutureWatcher<int>(this))
 {
diff --git a/colorcorrection/manager.cpp b/colorcorrection/manager.cpp
--- a/colorcorrection/manager.cpp
+++ b/colorcorrection/manager.cpp
@@ -94,7 +94,7 @@
 
     // Monitor for the time changing (flags == TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET).
     // However these are not exposed in glibc so value is hardcoded:
-    ::timerfd_settime(timeChangedFd, 3, &timespec, 0);
+    ::timerfd_settime(timeChangedFd, 3, &timespec, nullptr);
 
     connect(this, &QObject::destroyed, [timeChangedFd]() {
         ::close(timeChangedFd);
diff --git a/composite.h b/composite.h
--- a/composite.h
+++ b/composite.h
@@ -93,7 +93,7 @@
     virtual int refreshRate() const = 0;
 
     bool hasScene() const {
-        return m_scene != NULL;
+        return m_scene != nullptr;
     }
     Scene *scene() const {
         return m_scene;
@@ -110,7 +110,7 @@
      * @return bool @c true if there is a Compositor and it is active, @c false otherwise
      */
     static bool compositing() {
-        return s_compositor != NULL && s_compositor->isActive();
+        return s_compositor != nullptr && s_compositor->isActive();
     }
 
     // for delayed supportproperty management of effects
diff --git a/composite.cpp b/composite.cpp
--- a/composite.cpp
+++ b/composite.cpp
@@ -121,11 +121,11 @@
 Compositor::Compositor(QObject* workspace)
     : QObject(workspace)
     , m_state(State::Off)
-    , m_selectionOwner(NULL)
+    , m_selectionOwner(nullptr)
     , vBlankInterval(0)
     , fpsInterval(0)
     , m_timeSinceLastVBlank(0)
-    , m_scene(NULL)
+    , m_scene(nullptr)
     , m_bufferSwapPending(false)
     , m_composeAtSwapCompletion(false)
 {
@@ -176,7 +176,7 @@
     stop();
     deleteUnusedSupportProperties();
     destroyCompositorSelection();
-    s_compositor = NULL;
+    s_compositor = nullptr;
 }
 
 bool Compositor::setupStart()
@@ -250,12 +250,12 @@
         }
     }
 
-    if (m_scene == NULL || m_scene->initFailed()) {
+    if (m_scene == nullptr || m_scene->initFailed()) {
         qCCritical(KWIN_CORE) << "Failed to initialize compositing, compositing disabled";
         m_state = State::Off;
 
         delete m_scene;
-        m_scene = NULL;
+        m_scene = nullptr;
 
         if (m_selectionOwner) {
             m_selectionOwner->setOwning(false);
@@ -453,7 +453,7 @@
     }
 
     delete m_scene;
-    m_scene = NULL;
+    m_scene = nullptr;
     compositeTimer.stop();
     repaints_region = QRegion();
 
diff --git a/cursor.cpp b/cursor.cpp
--- a/cursor.cpp
+++ b/cursor.cpp
@@ -56,7 +56,7 @@
 
 Cursor::~Cursor()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 void Cursor::loadThemeSettings()
diff --git a/deleted.cpp b/deleted.cpp
--- a/deleted.cpp
+++ b/deleted.cpp
@@ -93,7 +93,7 @@
 
 void Deleted::copyToDeleted(Toplevel* c)
 {
-    Q_ASSERT(dynamic_cast< Deleted* >(c) == NULL);
+    Q_ASSERT(dynamic_cast< Deleted* >(c) == nullptr);
     Toplevel::copyToDeleted(c);
     desk = c->desktop();
     m_desktops = c->desktops();
diff --git a/effects.cpp b/effects.cpp
--- a/effects.cpp
+++ b/effects.cpp
@@ -104,7 +104,7 @@
     // get the atom for the propertyName
     ScopedCPointer<xcb_intern_atom_reply_t> atomReply(xcb_intern_atom_reply(c,
         xcb_intern_atom_unchecked(c, false, propertyName.size(), propertyName.constData()),
-        NULL));
+        nullptr));
     if (atomReply.isNull()) {
         return XCB_ATOM_NONE;
     }
@@ -119,8 +119,8 @@
 
 EffectsHandlerImpl::EffectsHandlerImpl(Compositor *compositor, Scene *scene)
     : EffectsHandler(scene->compositingType())
-    , keyboard_grab_effect(NULL)
-    , fullscreen_effect(0)
+    , keyboard_grab_effect(nullptr)
+    , fullscreen_effect(nullptr)
     , next_window_quad_type(EFFECT_QUAD_TYPE_START)
     , m_compositor(compositor)
     , m_scene(scene)
@@ -152,7 +152,7 @@
         [this](int old, AbstractClient *c) {
             const int newDesktop = VirtualDesktopManager::self()->current();
             if (old != 0 && newDesktop != old) {
-                emit desktopChanged(old, newDesktop, c ? c->effectWindow() : 0);
+                emit desktopChanged(old, newDesktop, c ? c->effectWindow() : nullptr);
                 // TODO: remove in 4.10
                 emit desktopChanged(old, newDesktop);
             }
@@ -466,7 +466,7 @@
     for (int i = 0; i < loaded_effects.size(); ++i)
         if (loaded_effects.at(i).second->provides(ef))
             return loaded_effects.at(i).second;
-    return NULL;
+    return nullptr;
 }
 
 void EffectsHandlerImpl::drawWindow(EffectWindow* w, int mask, QRegion region, WindowPaintData& data)
@@ -623,16 +623,16 @@
 {
     // during late cleanup effectWindow() may be already NULL
     // in some functions that may still call this
-    if (t == NULL || t->effectWindow() == NULL)
+    if (t == nullptr || t->effectWindow() == nullptr)
         return;
     emit windowGeometryShapeChanged(t->effectWindow(), old);
 }
 
 void EffectsHandlerImpl::slotPaddingChanged(Toplevel* t, const QRect& old)
 {
     // during late cleanup effectWindow() may be already NULL
     // in some functions that may still call this
-    if (t == NULL || t->effectWindow() == NULL)
+    if (t == nullptr || t->effectWindow() == nullptr)
         return;
     emit windowPaddingChanged(t->effectWindow(), old);
 }
@@ -662,7 +662,7 @@
 
 bool EffectsHandlerImpl::grabKeyboard(Effect* effect)
 {
-    if (keyboard_grab_effect != NULL)
+    if (keyboard_grab_effect != nullptr)
         return false;
     if (!doGrabKeyboard()) {
         return false;
@@ -678,18 +678,18 @@
 
 void EffectsHandlerImpl::ungrabKeyboard()
 {
-    Q_ASSERT(keyboard_grab_effect != NULL);
+    Q_ASSERT(keyboard_grab_effect != nullptr);
     doUngrabKeyboard();
-    keyboard_grab_effect = NULL;
+    keyboard_grab_effect = nullptr;
 }
 
 void EffectsHandlerImpl::doUngrabKeyboard()
 {
 }
 
 void EffectsHandlerImpl::grabbedKeyboardEvent(QKeyEvent* e)
 {
-    if (keyboard_grab_effect != NULL)
+    if (keyboard_grab_effect != nullptr)
         keyboard_grab_effect->grabbedKeyboardEvent(e);
 }
 
@@ -791,7 +791,7 @@
         if ((*it).first == name)
             return (*it).second->proxy();
 
-    return NULL;
+    return nullptr;
 }
 
 void EffectsHandlerImpl::startMousePolling()
@@ -808,7 +808,7 @@
 
 bool EffectsHandlerImpl::hasKeyboardGrab() const
 {
-    return keyboard_grab_effect != NULL;
+    return keyboard_grab_effect != nullptr;
 }
 
 void EffectsHandlerImpl::desktopResized(const QSize &size)
@@ -888,7 +888,7 @@
 
 EffectWindow* EffectsHandlerImpl::activeWindow() const
 {
-    return Workspace::self()->activeClient() ? Workspace::self()->activeClient()->effectWindow() : NULL;
+    return Workspace::self()->activeClient() ? Workspace::self()->activeClient()->effectWindow() : nullptr;
 }
 
 void EffectsHandlerImpl::moveWindow(EffectWindow* w, const QPoint& pos, bool snap, double snapAdjust)
@@ -1075,7 +1075,7 @@
             return w->effectWindow();
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 EffectWindow* EffectsHandlerImpl::findWindow(KWayland::Server::SurfaceInterface *surf) const
@@ -1210,7 +1210,7 @@
     if (auto c = TabBox::TabBox::self()->currentClient())
         return c->effectWindow();
 #endif
-    return NULL;
+    return nullptr;
 }
 
 void EffectsHandlerImpl::addRepaintFull()
@@ -2147,13 +2147,13 @@
 //****************************************
 
 EffectFrameImpl::EffectFrameImpl(EffectFrameStyle style, bool staticSize, QPoint position, Qt::Alignment alignment)
-    : QObject(0)
+    : QObject(nullptr)
     , EffectFrame()
     , m_style(style)
     , m_static(staticSize)
     , m_point(position)
     , m_alignment(alignment)
-    , m_shader(NULL)
+    , m_shader(nullptr)
     , m_theme(new Plasma::Theme(this))
 {
     if (m_style == EffectFrameStyled) {
@@ -2269,7 +2269,7 @@
     if (m_geometry.isEmpty()) {
         return; // Nothing to display
     }
-    m_shader = NULL;
+    m_shader = nullptr;
     setScreenProjectionMatrix(static_cast<EffectsHandlerImpl*>(effects)->scene()->screenProjectionMatrix());
     effects->paintEffectFrame(this, region, opacity, frameOpacity);
 }
diff --git a/effects/backgroundcontrast/contrastshader.cpp b/effects/backgroundcontrast/contrastshader.cpp
--- a/effects/backgroundcontrast/contrastshader.cpp
+++ b/effects/backgroundcontrast/contrastshader.cpp
@@ -34,7 +34,7 @@
 
 
 ContrastShader::ContrastShader()
-    : mValid(false), shader(NULL), m_opacity(1)
+    : mValid(false), shader(nullptr), m_opacity(1)
 {
 }
 
@@ -51,7 +51,7 @@
 void ContrastShader::reset()
 {
     delete shader;
-    shader = NULL;
+    shader = nullptr;
 
     setIsValid(false);
 }
diff --git a/effects/blur/blur_config.h b/effects/blur/blur_config.h
--- a/effects/blur/blur_config.h
+++ b/effects/blur/blur_config.h
@@ -31,7 +31,7 @@
     Q_OBJECT
 
 public:
-    explicit BlurEffectConfig(QWidget *parent = 0, const QVariantList& args = QVariantList());
+    explicit BlurEffectConfig(QWidget *parent = nullptr, const QVariantList& args = QVariantList());
     ~BlurEffectConfig() override;
 
     void save() override;
diff --git a/effects/coverswitch/coverswitch.h b/effects/coverswitch/coverswitch.h
--- a/effects/coverswitch/coverswitch.h
+++ b/effects/coverswitch/coverswitch.h
@@ -107,7 +107,7 @@
                     bool reflectedWindows = false);
     void paintWindowCover(EffectWindow* w, bool reflectedWindow, WindowPaintData& data);
     void paintFrontWindow(EffectWindow* frontWindow, int width, int leftWindows, int rightWindows, bool reflectedWindow);
-    void paintWindows(const EffectWindowList& windows, bool left, bool reflectedWindows, EffectWindow* additionalWindow = NULL);
+    void paintWindows(const EffectWindowList& windows, bool left, bool reflectedWindows, EffectWindow* additionalWindow = nullptr);
     void selectNextOrPreviousWindow(bool forward);
     inline void selectNextWindow() { selectNextOrPreviousWindow(true); }
     inline void selectPreviousWindow() { selectNextOrPreviousWindow(false); }
diff --git a/effects/coverswitch/coverswitch.cpp b/effects/coverswitch/coverswitch.cpp
--- a/effects/coverswitch/coverswitch.cpp
+++ b/effects/coverswitch/coverswitch.cpp
@@ -50,8 +50,8 @@
     , zPosition(900.0)
     , scaleFactor(0.0)
     , direction(Left)
-    , selected_window(0)
-    , captionFrame(NULL)
+    , selected_window(nullptr)
+    , captionFrame(nullptr)
     , primaryTabBox(false)
     , secondaryTabBox(false)
 {
@@ -65,7 +65,7 @@
     if (effects->compositingType() == OpenGL2Compositing) {
         m_reflectionShader = ShaderManager::instance()->generateShaderFromResources(ShaderTrait::MapTexture, QString(), QStringLiteral("coverswitch-reflection.glsl"));
     } else {
-        m_reflectionShader = NULL;
+        m_reflectionShader = nullptr;
     }
     connect(effects, &EffectsHandler::windowClosed, this, &CoverSwitchEffect::slotWindowClosed);
     connect(effects, &EffectsHandler::tabBoxAdded, this, &CoverSwitchEffect::slotTabBoxAdded);
@@ -123,7 +123,7 @@
         if (animation || start || stop) {
             timeLine.update(std::chrono::milliseconds(time));
         }
-        if (selected_window == NULL)
+        if (selected_window == nullptr)
             abort();
     }
     effects->prePaintScreen(data, time);
@@ -292,7 +292,7 @@
             timeLine.reset();
             if (stop) {
                 stop = false;
-                effects->setActiveFullScreenEffect(0);
+                effects->setActiveFullScreenEffect(nullptr);
                 foreach (EffectWindow * window, referrencedWindows) {
                     window->unrefWindow();
                 }
@@ -547,7 +547,7 @@
                 stopRequested = true;
             }
         } else {
-            effects->setActiveFullScreenEffect(0);
+            effects->setActiveFullScreenEffect(nullptr);
             start = false;
             animation = false;
             timeLine.reset();
@@ -565,7 +565,7 @@
         if (animateSwitch && currentWindowList.count() > 1) {
             // determine the switch direction
             if (selected_window != effects->currentTabBoxWindow()) {
-                if (selected_window != NULL) {
+                if (selected_window != nullptr) {
                     int old_index = currentWindowList.indexOf(selected_window);
                     int new_index = effects->currentTabBoxWindowList().indexOf(effects->currentTabBoxWindow());
                     Direction new_direction;
@@ -701,7 +701,7 @@
 
 void CoverSwitchEffect::paintFrontWindow(EffectWindow* frontWindow, int width, int leftWindows, int rightWindows, bool reflectedWindow)
 {
-    if (frontWindow == NULL)
+    if (frontWindow == nullptr)
         return;
     bool specialHandlingForward = false;
     WindowPaintData data(frontWindow);
@@ -764,7 +764,7 @@
         xTranslate = ((float)screenSize.width() * 0.5 * scaleFactor) - (float)width * 0.5f;
     // handling for additional window from other side
     // has to appear on this side after half of the time
-    if (animation && timeLine.value() >= 0.5 && additionalWindow != NULL) {
+    if (animation && timeLine.value() >= 0.5 && additionalWindow != nullptr) {
         WindowPaintData data(additionalWindow);
         if (effects->numScreens() > 1) {
             data.setProjectionMatrix(m_projectionMatrix);
@@ -786,7 +786,7 @@
     // normal behaviour
     for (int i = 0; i < windows.count(); i++) {
         window = windows.at(i);
-        if (window == NULL || window->isDeleted()) {
+        if (window == nullptr || window->isDeleted()) {
             continue;
         }
         WindowPaintData data(window);
@@ -918,7 +918,7 @@
         effects->unrefTabBox();
         effects->stopMouseInterception(this);
     }
-    effects->setActiveFullScreenEffect(0);
+    effects->setActiveFullScreenEffect(nullptr);
     timeLine.reset();
     mActivated = false;
     stop = false;
@@ -930,7 +930,7 @@
 void CoverSwitchEffect::slotWindowClosed(EffectWindow* c)
 {
     if (c == selected_window)
-        selected_window = 0;
+        selected_window = nullptr;
     // if the list is not empty, the effect is active
     if (!currentWindowList.isEmpty()) {
         c->refWindow();
diff --git a/effects/coverswitch/coverswitch_config.h b/effects/coverswitch/coverswitch_config.h
--- a/effects/coverswitch/coverswitch_config.h
+++ b/effects/coverswitch/coverswitch_config.h
@@ -40,7 +40,7 @@
 {
     Q_OBJECT
 public:
-    explicit CoverSwitchEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit CoverSwitchEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/cube/cube.cpp b/effects/cube/cube.cpp
--- a/effects/cube/cube.cpp
+++ b/effects/cube/cube.cpp
@@ -56,13 +56,13 @@
     , cubeOpacity(1.0)
     , opacityDesktopOnly(true)
     , displayDesktopName(false)
-    , desktopNameFrame(NULL)
+    , desktopNameFrame(nullptr)
     , reflection(true)
     , desktopChangedWhileRotating(false)
     , paintCaps(true)
-    , wallpaper(NULL)
+    , wallpaper(nullptr)
     , texturedCaps(true)
-    , capTexture(NULL)
+    , capTexture(nullptr)
     , reflectionPainting(false)
     , activeScreen(0)
     , bottomCap(false)
@@ -74,12 +74,12 @@
     , shortcutsRegistered(false)
     , mode(Cube)
     , useShaders(false)
-    , cylinderShader(0)
-    , sphereShader(0)
+    , cylinderShader(nullptr)
+    , sphereShader(nullptr)
     , zOrderingFactor(0.0f)
     , mAddedHeightCoeff1(0.0f)
     , mAddedHeightCoeff2(0.0f)
-    , m_cubeCapBuffer(NULL)
+    , m_cubeCapBuffer(nullptr)
     , m_proxy(this)
     , m_cubeAction(new QAction(this))
     , m_cylinderAction(new QAction(this))
@@ -93,8 +93,8 @@
         m_reflectionShader = ShaderManager::instance()->generateShaderFromResources(ShaderTrait::MapTexture, QString(), QStringLiteral("cube-reflection.glsl"));
         m_capShader = ShaderManager::instance()->generateShaderFromResources(ShaderTrait::MapTexture, QString(), QStringLiteral("cube-cap.glsl"));
     } else {
-        m_reflectionShader = NULL;
-        m_capShader = NULL;
+        m_reflectionShader = nullptr;
+        m_capShader = nullptr;
     }
     m_textureMirrorMatrix.scale(1.0, -1.0, 1.0);
     m_textureMirrorMatrix.translate(0.0, -1.0, 0.0);
@@ -179,9 +179,9 @@
     capDeformationFactor = (float)CubeConfig::capDeformation() / 100.0f;
     useZOrdering = CubeConfig::zOrdering();
     delete wallpaper;
-    wallpaper = NULL;
+    wallpaper = nullptr;
     delete capTexture;
-    capTexture = NULL;
+    capTexture = nullptr;
     texturedCaps = CubeConfig::texturedCaps();
 
     timeLine.setEasingCurve(QEasingCurve::InOutSine);
@@ -282,7 +282,7 @@
         }
         // need to recreate the VBO for the cube cap
         delete m_cubeCapBuffer;
-        m_cubeCapBuffer = NULL;
+        m_cubeCapBuffer = nullptr;
         effects->addRepaintFull();
     }
     watcher->deleteLater();
@@ -844,7 +844,7 @@
     }
     delete m_cubeCapBuffer;
     m_cubeCapBuffer = new GLVertexBuffer(GLVertexBuffer::Static);
-    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : NULL);
+    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : nullptr);
 }
 
 void CubeEffect::paintCylinderCap()
@@ -899,7 +899,7 @@
     }
     delete m_cubeCapBuffer;
     m_cubeCapBuffer = new GLVertexBuffer(GLVertexBuffer::Static);
-    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : NULL);
+    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : nullptr);
 }
 
 void CubeEffect::paintSphereCap()
@@ -956,7 +956,7 @@
     }
     delete m_cubeCapBuffer;
     m_cubeCapBuffer = new GLVertexBuffer(GLVertexBuffer::Static);
-    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : NULL);
+    m_cubeCapBuffer->setData(verts.count() / 3, 3, verts.constData(), texture ? texCoords.constData() : nullptr);
 }
 
 void CubeEffect::postPaintScreen()
@@ -975,9 +975,9 @@
             keyboard_grab = false;
             effects->stopMouseInterception(this);
             effects->setCurrentDesktop(frontDesktop);
-            effects->setActiveFullScreenEffect(0);
+            effects->setActiveFullScreenEffect(nullptr);
             delete m_cubeCapBuffer;
-            m_cubeCapBuffer = NULL;
+            m_cubeCapBuffer = nullptr;
             if (desktopNameFrame)
                 desktopNameFrame->free();
             activated = false;
@@ -1314,7 +1314,7 @@
                 QColor color = capColor;
                 capColor.setAlphaF(cubeOpacity);
                 vbo->setColor(color);
-                vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+                vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
                 if (!capShader || mode == Cube) {
                     // TODO: use sphere and cylinder shaders
                     vbo->render(GL_TRIANGLES);
diff --git a/effects/cube/cube_config.h b/effects/cube/cube_config.h
--- a/effects/cube/cube_config.h
+++ b/effects/cube/cube_config.h
@@ -40,7 +40,7 @@
 {
     Q_OBJECT
 public:
-    explicit CubeEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit CubeEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/cubeslide/cubeslide.cpp b/effects/cubeslide/cubeslide.cpp
--- a/effects/cubeslide/cubeslide.cpp
+++ b/effects/cubeslide/cubeslide.cpp
@@ -387,7 +387,7 @@
                     w->setData(WindowForceBackgroundContrastRole, QVariant());
                 }
                 staticWindows.clear();
-                effects->setActiveFullScreenEffect(0);
+                effects->setActiveFullScreenEffect(nullptr);
             }
         }
         effects->addRepaintFull();
@@ -586,7 +586,7 @@
         timeLine.setCurrentTime(0);
         if (!slideRotations.isEmpty())
             slideRotations.clear();
-        effects->setActiveFullScreenEffect(0);
+        effects->setActiveFullScreenEffect(nullptr);
         effects->addRepaintFull();
     }
 }
diff --git a/effects/cubeslide/cubeslide_config.h b/effects/cubeslide/cubeslide_config.h
--- a/effects/cubeslide/cubeslide_config.h
+++ b/effects/cubeslide/cubeslide_config.h
@@ -40,7 +40,7 @@
 {
     Q_OBJECT
 public:
-    explicit CubeSlideEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit CubeSlideEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/desktopgrid/desktopgrid.h b/effects/desktopgrid/desktopgrid.h
--- a/effects/desktopgrid/desktopgrid.h
+++ b/effects/desktopgrid/desktopgrid.h
@@ -36,7 +36,7 @@
 {
     Q_OBJECT
 public:
-    explicit DesktopButtonsView(QWindow *parent = 0);
+    explicit DesktopButtonsView(QWindow *parent = nullptr);
     void windowInputMouseEvent(QMouseEvent* e);
     void setAddDesktopEnabled(bool enable);
     void setRemoveDesktopEnabled(bool enable);
@@ -119,7 +119,7 @@
 
 private:
     QPointF scalePos(const QPoint& pos, int desktop, int screen = -1) const;
-    QPoint unscalePos(const QPoint& pos, int* desktop = NULL) const;
+    QPoint unscalePos(const QPoint& pos, int* desktop = nullptr) const;
     int posToDesktop(const QPoint& pos) const;
     EffectWindow* windowAt(QPoint pos) const;
     void setCurrentDesktop(int desktop);
diff --git a/effects/desktopgrid/desktopgrid.cpp b/effects/desktopgrid/desktopgrid.cpp
--- a/effects/desktopgrid/desktopgrid.cpp
+++ b/effects/desktopgrid/desktopgrid.cpp
@@ -57,16 +57,16 @@
     , wasWindowCopy(false)
     , wasDesktopMove(false)
     , isValidMove(false)
-    , windowMove(NULL)
+    , windowMove(nullptr)
     , windowMoveDiff()
     , gridSize()
     , orientation(Qt::Horizontal)
     , activeCell(1, 1)
     , scale()
     , unscaledBorder()
     , scaledSize()
     , scaledOffset()
-    , m_proxy(0)
+    , m_proxy(nullptr)
     , m_activateAction(new QAction(this))
 {
     initConfig<DesktopGridConfig>();
@@ -428,7 +428,7 @@
         return;
     if (w == windowMove) {
         effects->setElevatedWindow(windowMove, false);
-        windowMove = NULL;
+        windowMove = nullptr;
     }
     if (isUsingPresentWindows()) {
         foreach (const int i, desktopList(w)) {
@@ -443,7 +443,7 @@
 void DesktopGridEffect::slotWindowDeleted(EffectWindow* w)
 {
     if (w == windowMove)
-        windowMove = 0;
+        windowMove = nullptr;
     foreach (DesktopButtonsView *view, m_desktopButtonsViews) {
         if (view->effectWindow && view->effectWindow == w) {
             view->effectWindow = nullptr;
@@ -494,7 +494,7 @@
 
     if (e->type() == QEvent::MouseMove) {
         int d = posToDesktop(me->pos());
-        if (windowMove != NULL &&
+        if (windowMove != nullptr &&
                 (me->pos() - dragStartPos).manhattanLength() > QApplication::startDragDistance()) {
             // Handle window moving
             if (!wasWindowMove) { // Activate on move
@@ -522,7 +522,7 @@
             if (windowMove->isMovable() && !isUsingPresentWindows()) {
                 wasWindowMove = true;
                 int screen = effects->screenNumber(me->pos());
-                effects->moveWindow(windowMove, unscalePos(me->pos(), NULL) + windowMoveDiff, true, 1.0 / scale[screen]);
+                effects->moveWindow(windowMove, unscalePos(me->pos(), nullptr) + windowMoveDiff, true, 1.0 / scale[screen]);
             }
             if (wasWindowMove) {
                 if (effects->waylandDisplay() && (me->modifiers() & Qt::ControlModifier)) {
@@ -603,25 +603,25 @@
             dragStartPos = me->pos();
             sourceDesktop = posToDesktop(me->pos());
             bool isDesktop = (me->modifiers() & Qt::ShiftModifier);
-            EffectWindow* w = isDesktop ? NULL : windowAt(me->pos());
-            if (w != NULL)
+            EffectWindow* w = isDesktop ? nullptr : windowAt(me->pos());
+            if (w != nullptr)
                 isDesktop = w->isDesktop();
             if (isDesktop)
                 m_originalMovingDesktop = posToDesktop(me->pos());
             else
                 m_originalMovingDesktop = 0;
-            if (w != NULL && !w->isDesktop() && (w->isMovable() || w->isMovableAcrossScreens() || isUsingPresentWindows())) {
+            if (w != nullptr && !w->isDesktop() && (w->isMovable() || w->isMovableAcrossScreens() || isUsingPresentWindows())) {
                 // Prepare it for moving
-                windowMoveDiff = w->pos() - unscalePos(me->pos(), NULL);
+                windowMoveDiff = w->pos() - unscalePos(me->pos(), nullptr);
                 windowMove = w;
                 effects->setElevatedWindow(windowMove, true);
             }
-        } else if ((me->buttons() == Qt::MidButton || me->buttons() == Qt::RightButton) && windowMove == NULL) {
+        } else if ((me->buttons() == Qt::MidButton || me->buttons() == Qt::RightButton) && windowMove == nullptr) {
             EffectWindow* w = windowAt(me->pos());
             if (w && w->isDesktop()) {
                 w = nullptr;
             }
-            if (w != NULL) {
+            if (w != nullptr) {
                 const int desktop = posToDesktop(me->pos());
                 if (w->isOnAllDesktops()) {
                     effects->windowToDesktop(w, desktop);
@@ -675,7 +675,7 @@
                 effects->addRepaintFull();
             }
             effects->setElevatedWindow(windowMove, false);
-            windowMove = NULL;
+            windowMove = nullptr;
         }
         wasWindowMove = false;
         wasWindowCopy = false;
@@ -687,7 +687,7 @@
 {
     if (timeline.currentValue() != 1)   // Block user input during animations
         return;
-    if (windowMove != NULL)
+    if (windowMove != nullptr)
         return;
     if (e->type() == QEvent::KeyPress) {
         // check for global shortcuts
@@ -823,7 +823,7 @@
     int gy = qBound(0, int(scaledY), gridSize.height() - 1);
     scaledX -= gx;
     scaledY -= gy;
-    if (desktop != NULL) {
+    if (desktop != nullptr) {
         if (orientation == Qt::Horizontal)
             *desktop = gy * gridSize.width() + gx + 1;
         else
@@ -879,7 +879,7 @@
     int desktop;
     pos = unscalePos(pos, &desktop);
     if (desktop > effects->numberOfDesktops())
-        return NULL;
+        return nullptr;
     if (isUsingPresentWindows()) {
         const int screen = effects->screenNumber(pos);
         EffectWindow *w =
@@ -896,7 +896,7 @@
                 return w;
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 void DesktopGridEffect::setCurrentDesktop(int desktop)
@@ -1223,13 +1223,13 @@
         effects->ungrabKeyboard();
     keyboardGrab = false;
     effects->stopMouseInterception(this);
-    effects->setActiveFullScreenEffect(0);
+    effects->setActiveFullScreenEffect(nullptr);
     if (isUsingPresentWindows()) {
         while (!m_managers.isEmpty()) {
             m_managers.first().unmanageAll();
             m_managers.removeFirst();
         }
-        m_proxy = 0;
+        m_proxy = nullptr;
     }
 }
 
@@ -1256,7 +1256,7 @@
 
 bool DesktopGridEffect::isUsingPresentWindows() const
 {
-    return (m_proxy != NULL);
+    return (m_proxy != nullptr);
 }
 
 // transforms the geometry of the moved window to a geometry on the desktop
diff --git a/effects/desktopgrid/desktopgrid_config.h b/effects/desktopgrid/desktopgrid_config.h
--- a/effects/desktopgrid/desktopgrid_config.h
+++ b/effects/desktopgrid/desktopgrid_config.h
@@ -41,7 +41,7 @@
 {
     Q_OBJECT
 public:
-    explicit DesktopGridEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit DesktopGridEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~DesktopGridEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/flipswitch/flipswitch.cpp b/effects/flipswitch/flipswitch.cpp
--- a/effects/flipswitch/flipswitch.cpp
+++ b/effects/flipswitch/flipswitch.cpp
@@ -45,7 +45,7 @@
     , m_stop(false)
     , m_animation(false)
     , m_hasKeyboardGrab(false)
-    , m_captionFrame(NULL)
+    , m_captionFrame(nullptr)
 {
     initConfig<FlipSwitchConfig>();
     reconfigure(ReconfigureAll);
@@ -153,7 +153,7 @@
                     index = index % tempList.count();
             }
             tabIndex = index;
-            EffectWindow* w = NULL;
+            EffectWindow* w = nullptr;
             if (!m_scheduledDirections.isEmpty() && m_scheduledDirections.head() == DirectionBackward) {
                 index--;
                 if (index < 0)
@@ -180,7 +180,7 @@
                     index = 0;
             }
             tabIndex = index;
-            EffectWindow* w = NULL;
+            EffectWindow* w = nullptr;
             if (!m_scheduledDirections.isEmpty() && m_scheduledDirections.head() == DirectionBackward) {
                 index++;
                 if (index >= tempList.count())
@@ -331,7 +331,7 @@
             m_stop = false;
             m_active = false;
             m_captionFrame->free();
-            effects->setActiveFullScreenEffect(0);
+            effects->setActiveFullScreenEffect(nullptr);
             effects->addRepaintFull();
             qDeleteAll(m_windows);
             m_windows.clear();
@@ -439,7 +439,7 @@
         if (!effects->currentTabBoxWindowList().isEmpty()) {
             // determine the switch direction
             if (m_selectedWindow != effects->currentTabBoxWindow()) {
-                if (m_selectedWindow != NULL) {
+                if (m_selectedWindow != nullptr) {
                     int old_index = effects->currentTabBoxWindowList().indexOf(m_selectedWindow);
                     int new_index = effects->currentTabBoxWindowList().indexOf(effects->currentTabBoxWindow());
                     SwitchingDirection new_direction;
@@ -487,7 +487,7 @@
 void FlipSwitchEffect::slotWindowClosed(EffectWindow* w)
 {
     if (m_selectedWindow == w)
-        m_selectedWindow = 0;
+        m_selectedWindow = nullptr;
     if (m_active) {
         QHash< const EffectWindow*, ItemInfo* >::iterator it = m_windows.find(w);
         if (it != m_windows.end()) {
diff --git a/effects/flipswitch/flipswitch_config.h b/effects/flipswitch/flipswitch_config.h
--- a/effects/flipswitch/flipswitch_config.h
+++ b/effects/flipswitch/flipswitch_config.h
@@ -41,7 +41,7 @@
 {
     Q_OBJECT
 public:
-    explicit FlipSwitchEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit FlipSwitchEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~FlipSwitchEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/highlightwindow/highlightwindow.h b/effects/highlightwindow/highlightwindow.h
--- a/effects/highlightwindow/highlightwindow.h
+++ b/effects/highlightwindow/highlightwindow.h
@@ -49,7 +49,7 @@
     void slotWindowAdded(KWin::EffectWindow* w);
     void slotWindowClosed(KWin::EffectWindow *w);
     void slotWindowDeleted(KWin::EffectWindow *w);
-    void slotPropertyNotify(KWin::EffectWindow* w, long atom, EffectWindow *addedWindow = NULL);
+    void slotPropertyNotify(KWin::EffectWindow* w, long atom, EffectWindow *addedWindow = nullptr);
 
 private:
     void prepareHighlighting();
diff --git a/effects/highlightwindow/highlightwindow.cpp b/effects/highlightwindow/highlightwindow.cpp
--- a/effects/highlightwindow/highlightwindow.cpp
+++ b/effects/highlightwindow/highlightwindow.cpp
@@ -26,7 +26,7 @@
 HighlightWindowEffect::HighlightWindowEffect()
     : m_finishing(false)
     , m_fadeDuration(float(animationTime(150)))
-    , m_monitorWindow(NULL)
+    , m_monitorWindow(nullptr)
 {
     m_atom = effects->announceSupportProperty("_KDE_WINDOW_HIGHLIGHT", this);
     connect(effects, &EffectsHandler::windowAdded, this, &HighlightWindowEffect::slotWindowAdded);
@@ -261,7 +261,7 @@
 void HighlightWindowEffect::finishHighlighting()
 {
     m_finishing = true;
-    m_monitorWindow = NULL;
+    m_monitorWindow = nullptr;
     m_highlightedWindows.clear();
     if (!m_windowOpacity.isEmpty())
         m_windowOpacity.constBegin().key()->addRepaintFull();
diff --git a/effects/invert/invert.cpp b/effects/invert/invert.cpp
--- a/effects/invert/invert.cpp
+++ b/effects/invert/invert.cpp
@@ -37,7 +37,7 @@
 InvertEffect::InvertEffect()
     :   m_inited(false),
         m_valid(true),
-        m_shader(NULL),
+        m_shader(nullptr),
         m_allWindows(false)
 {
     QAction* a = new QAction(this);
diff --git a/effects/invert/invert_config.h b/effects/invert/invert_config.h
--- a/effects/invert/invert_config.h
+++ b/effects/invert/invert_config.h
@@ -32,7 +32,7 @@
 {
     Q_OBJECT
 public:
-    explicit InvertEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit InvertEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~InvertEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/lookingglass/lookingglass.cpp b/effects/lookingglass/lookingglass.cpp
--- a/effects/lookingglass/lookingglass.cpp
+++ b/effects/lookingglass/lookingglass.cpp
@@ -45,10 +45,10 @@
     : zoom(1.0f)
     , target_zoom(1.0f)
     , polling(false)
-    , m_texture(NULL)
-    , m_fbo(NULL)
-    , m_vbo(NULL)
-    , m_shader(NULL)
+    , m_texture(nullptr)
+    , m_fbo(nullptr)
+    , m_vbo(nullptr)
+    , m_shader(nullptr)
     , m_enabled(false)
     , m_valid(false)
 {
diff --git a/effects/lookingglass/lookingglass_config.h b/effects/lookingglass/lookingglass_config.h
--- a/effects/lookingglass/lookingglass_config.h
+++ b/effects/lookingglass/lookingglass_config.h
@@ -41,7 +41,7 @@
 {
     Q_OBJECT
 public:
-    explicit LookingGlassEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit LookingGlassEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~LookingGlassEffectConfig() override;
 
     void save() override;
diff --git a/effects/magiclamp/magiclamp.cpp b/effects/magiclamp/magiclamp.cpp
--- a/effects/magiclamp/magiclamp.cpp
+++ b/effects/magiclamp/magiclamp.cpp
@@ -134,7 +134,7 @@
             icon = QRect(pt, QSize(0, 0));
         } else {
             // Assumption: there is a panel containing the icon position
-            EffectWindow* panel = NULL;
+            EffectWindow* panel = nullptr;
             foreach (EffectWindow * window, effects->stackingOrder()) {
                 if (!window->isDock())
                     continue;
diff --git a/effects/magiclamp/magiclamp_config.h b/effects/magiclamp/magiclamp_config.h
--- a/effects/magiclamp/magiclamp_config.h
+++ b/effects/magiclamp/magiclamp_config.h
@@ -40,7 +40,7 @@
 {
     Q_OBJECT
 public:
-    explicit MagicLampEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit MagicLampEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/magnifier/magnifier.cpp b/effects/magnifier/magnifier.cpp
--- a/effects/magnifier/magnifier.cpp
+++ b/effects/magnifier/magnifier.cpp
@@ -44,8 +44,8 @@
     : zoom(1)
     , target_zoom(1)
     , polling(false)
-    , m_texture(0)
-    , m_fbo(0)
+    , m_texture(nullptr)
+    , m_fbo(nullptr)
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
     , m_pixmap(XCB_PIXMAP_NONE)
 #endif
@@ -127,8 +127,8 @@
                 // zoom ended - delete FBO and texture
                 delete m_fbo;
                 delete m_texture;
-                m_fbo = NULL;
-                m_texture = NULL;
+                m_fbo = nullptr;
+                m_texture = nullptr;
                 destroyPixmap();
             }
         }
@@ -195,7 +195,7 @@
             verts << areaF.left() - FRAME_WIDTH << areaF.bottom() + FRAME_WIDTH;
             verts << areaF.right() + FRAME_WIDTH << areaF.bottom() + FRAME_WIDTH;
             verts << areaF.right() + FRAME_WIDTH << areaF.bottom();
-            vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+            vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
 
             ShaderBinder binder(ShaderTrait::UniformColor);
             binder.shader()->setUniform(GLShader::ModelViewProjectionMatrix, data.projectionMatrix());
@@ -228,10 +228,10 @@
             xform.matrix22 = DOUBLE_TO_FIXED(1.0/zoom);
 #undef DOUBLE_TO_FIXED
             xcb_render_set_picture_transform(xcbConnection(), *m_picture, xform);
-            xcb_render_set_picture_filter(xcbConnection(), *m_picture, 4, const_cast<char*>("good"), 0, NULL);
+            xcb_render_set_picture_filter(xcbConnection(), *m_picture, 4, const_cast<char*>("good"), 0, nullptr);
             xcb_render_composite(xcbConnection(), XCB_RENDER_PICT_OP_SRC, *m_picture, 0, effects->xrenderBufferPicture(),
                                  0, 0, 0, 0, area.x(), area.y(), area.width(), area.height() );
-            xcb_render_set_picture_filter(xcbConnection(), *m_picture, 4, const_cast<char*>("fast"), 0, NULL);
+            xcb_render_set_picture_filter(xcbConnection(), *m_picture, 4, const_cast<char*>("fast"), 0, nullptr);
             xcb_render_set_picture_transform(xcbConnection(), *m_picture, identity);
             const xcb_rectangle_t rects[4] = {
                 { int16_t(area.x()+FRAME_WIDTH), int16_t(area.y()), uint16_t(area.width()-FRAME_WIDTH), uint16_t(FRAME_WIDTH)},
@@ -290,8 +290,8 @@
             effects->makeOpenGLContextCurrent();
             delete m_fbo;
             delete m_texture;
-            m_fbo = NULL;
-            m_texture = NULL;
+            m_fbo = nullptr;
+            m_texture = nullptr;
             destroyPixmap();
         }
     }
diff --git a/effects/magnifier/magnifier_config.h b/effects/magnifier/magnifier_config.h
--- a/effects/magnifier/magnifier_config.h
+++ b/effects/magnifier/magnifier_config.h
@@ -41,7 +41,7 @@
 {
     Q_OBJECT
 public:
-    explicit MagnifierEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit MagnifierEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~MagnifierEffectConfig() override;
 
     void save() override;
diff --git a/effects/mouseclick/mouseclick.cpp b/effects/mouseclick/mouseclick.cpp
--- a/effects/mouseclick/mouseclick.cpp
+++ b/effects/mouseclick/mouseclick.cpp
@@ -164,7 +164,7 @@
     if (buttons == oldButtons)
         return;
 
-    MouseEvent* m = NULL;
+    MouseEvent* m = nullptr;
     int i = BUTTON_COUNT;
     while (--i >= 0) {
         MouseButton* b = m_buttons[i];
@@ -187,7 +187,7 @@
 
 EffectFrame* MouseClickEffect::createEffectFrame(const QPoint& pos, const QString& text) {
     if (!m_showText) {
-        return NULL;
+        return nullptr;
     }
     QPoint point(pos.x() + m_ringMaxSize, pos.y());
     EffectFrame* frame = effects->effectFrame(EffectFrameStyled, false, point, Qt::AlignLeft);
@@ -295,7 +295,7 @@
         x = c * x - s * y;
         y = s * t + c * y;
     }
-    vbo->setData(verts.size() / 2, 2, verts.data(), NULL);
+    vbo->setData(verts.size() / 2, 2, verts.data(), nullptr);
     vbo->render(GL_LINE_LOOP);
 }
 
diff --git a/effects/mouseclick/mouseclick_config.h b/effects/mouseclick/mouseclick_config.h
--- a/effects/mouseclick/mouseclick_config.h
+++ b/effects/mouseclick/mouseclick_config.h
@@ -41,7 +41,7 @@
 {
     Q_OBJECT
 public:
-    explicit MouseClickEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit MouseClickEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~MouseClickEffectConfig() override;
 
     void save() override;
diff --git a/effects/mousemark/mousemark.cpp b/effects/mousemark/mousemark.cpp
--- a/effects/mousemark/mousemark.cpp
+++ b/effects/mousemark/mousemark.cpp
@@ -138,16 +138,16 @@
             foreach (const QPoint & p, mark) {
                 verts << p.x() << p.y();
             }
-            vbo->setData(verts.size() / 2, 2, verts.data(), NULL);
+            vbo->setData(verts.size() / 2, 2, verts.data(), nullptr);
             vbo->render(GL_LINE_STRIP);
         }
         if (!drawing.isEmpty()) {
             verts.clear();
             verts.reserve(drawing.size() * 2);
             foreach (const QPoint & p, drawing) {
                 verts << p.x() << p.y();
             }
-            vbo->setData(verts.size() / 2, 2, verts.data(), NULL);
+            vbo->setData(verts.size() / 2, 2, verts.data(), nullptr);
             vbo->render(GL_LINE_STRIP);
         }
         glLineWidth(1.0);
diff --git a/effects/mousemark/mousemark_config.h b/effects/mousemark/mousemark_config.h
--- a/effects/mousemark/mousemark_config.h
+++ b/effects/mousemark/mousemark_config.h
@@ -41,7 +41,7 @@
 {
     Q_OBJECT
 public:
-    explicit MouseMarkEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit MouseMarkEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~MouseMarkEffectConfig() override;
 
     void save() override;
diff --git a/effects/presentwindows/presentwindows.h b/effects/presentwindows/presentwindows.h
--- a/effects/presentwindows/presentwindows.h
+++ b/effects/presentwindows/presentwindows.h
@@ -36,7 +36,7 @@
 {
     Q_OBJECT
 public:
-    explicit CloseWindowView(QObject *parent = 0);
+    explicit CloseWindowView(QObject *parent = nullptr);
     void windowInputMouseEvent(QMouseEvent* e);
     void disarm();
 
diff --git a/effects/presentwindows/presentwindows.cpp b/effects/presentwindows/presentwindows.cpp
--- a/effects/presentwindows/presentwindows.cpp
+++ b/effects/presentwindows/presentwindows.cpp
@@ -56,12 +56,12 @@
     , m_decalOpacity(0.0)
     , m_hasKeyboardGrab(false)
     , m_mode(ModeCurrentDesktop)
-    , m_managerWindow(NULL)
+    , m_managerWindow(nullptr)
     , m_needInitialSelection(false)
-    , m_highlightedWindow(NULL)
-    , m_filterFrame(NULL)
-    , m_closeView(NULL)
-    , m_closeWindow(NULL)
+    , m_highlightedWindow(nullptr)
+    , m_filterFrame(nullptr)
+    , m_closeView(nullptr)
+    , m_closeWindow(nullptr)
     , m_exposeAction(new QAction(this))
     , m_exposeAllAction(new QAction(this))
     , m_exposeClassAction(new QAction(this))
@@ -251,7 +251,7 @@
             w->setData(WindowForceBlurRole, QVariant());
             w->setData(WindowForceBackgroundContrastRole, QVariant());
         }
-        effects->setActiveFullScreenEffect(NULL);
+        effects->setActiveFullScreenEffect(nullptr);
         effects->addRepaintFull();
     } else if (m_activated && m_needInitialSelection) {
         m_needInitialSelection = false;
@@ -328,7 +328,7 @@
                 winData->referenced = false;
                 w->unrefWindow();
                 if (w == m_closeWindow) {
-                    m_closeWindow = NULL;
+                    m_closeWindow = nullptr;
                 }
             } else
                 w->enablePainting(EffectWindow::PAINT_DISABLED_BY_DELETE);
@@ -490,7 +490,7 @@
 void PresentWindowsEffect::slotWindowClosed(EffectWindow *w)
 {
     if (m_managerWindow == w)
-        m_managerWindow = NULL;
+        m_managerWindow = nullptr;
     DataHash::iterator winData = m_windowData.find(w);
     if (winData == m_windowData.end())
         return;
@@ -592,7 +592,7 @@
     // We cannot use m_motionManager.windowAtPoint() as the window might not be visible
     EffectWindowList windows = m_motionManager.managedWindows();
     bool hovering = false;
-    EffectWindow *highlightCandidate = NULL;
+    EffectWindow *highlightCandidate = nullptr;
     for (int i = 0; i < windows.size(); ++i) {
         DataHash::const_iterator winData = m_windowData.constFind(windows.at(i));
         if (winData == m_windowData.constEnd())
@@ -606,7 +606,7 @@
         }
     }
     if (!hovering)
-        setHighlightedWindow(NULL);
+        setHighlightedWindow(nullptr);
     if (m_highlightedWindow && m_motionManager.transformedGeometry(m_highlightedWindow).contains(pos))
         updateCloseWindow();
     else if (m_closeView)
@@ -954,7 +954,7 @@
         }
     }
     if (windowlist.isEmpty()) {
-        setHighlightedWindow(NULL);
+        setHighlightedWindow(nullptr);
         return;
     }
 
@@ -989,7 +989,7 @@
     }
 
     // Resize text frames if required
-    QFontMetrics* metrics = NULL; // All fonts are the same
+    QFontMetrics* metrics = nullptr; // All fonts are the same
     foreach (EffectWindow * w, m_motionManager.managedWindows()) {
         DataHash::iterator winData = m_windowData.find(w);
         if (winData == m_windowData.end())
@@ -1537,7 +1537,7 @@
         m_needInitialSelection = true;
         m_closeButtonCorner = (Qt::Corner)effects->kwinOption(KWin::CloseButtonCorner).toInt();
         m_decalOpacity = 0.0;
-        m_highlightedWindow = NULL;
+        m_highlightedWindow = nullptr;
         m_windowFilter.clear();
 
         if (!(m_doNotCloseWindows || m_closeView)) {
@@ -1646,7 +1646,7 @@
                 m_managerWindow->deleteProperty(m_atomDesktop);
             else if (m_mode == ModeWindowGroup && m_atomWindows != XCB_ATOM_NONE)
                 m_managerWindow->deleteProperty(m_atomWindows);
-            m_managerWindow = NULL;
+            m_managerWindow = nullptr;
         }
     }
     effects->addRepaintFull(); // Trigger the first repaint
@@ -1714,7 +1714,7 @@
 
 void PresentWindowsEffect::setHighlightedWindow(EffectWindow *w)
 {
-    if (w == m_highlightedWindow || (w != NULL && !m_motionManager.isManaging(w)))
+    if (w == m_highlightedWindow || (w != nullptr && !m_motionManager.isManaging(w)))
         return;
 
     if (m_closeView)
@@ -1805,24 +1805,24 @@
             for (int i = 0; i < xdiff; i++) {
                 QRectF wArea = m_motionManager.transformedGeometry(w);
                 detectRect = QRect(0, wArea.y(), area.width(), wArea.height());
-                next = NULL;
+                next = nullptr;
                 foreach (EffectWindow * e, m_motionManager.managedWindows()) {
                     DataHash::const_iterator winData = m_windowData.find(e);
                     if (winData == m_windowData.end() || !winData->visible)
                         continue;
                     QRectF eArea = m_motionManager.transformedGeometry(e);
                     if (eArea.intersects(detectRect) &&
                             eArea.x() > wArea.x()) {
-                        if (next == NULL)
+                        if (next == nullptr)
                             next = e;
                         else {
                             QRectF nArea = m_motionManager.transformedGeometry(next);
                             if (eArea.x() < nArea.x())
                                 next = e;
                         }
                     }
                 }
-                if (next == NULL) {
+                if (next == nullptr) {
                     if (wrap)   // We are at the right-most window, now get the left-most one to wrap
                         return relativeWindow(w, -1000, 0, false);
                     break; // No more windows to the right
@@ -1835,24 +1835,24 @@
             for (int i = 0; i < -xdiff; i++) {
                 QRectF wArea = m_motionManager.transformedGeometry(w);
                 detectRect = QRect(0, wArea.y(), area.width(), wArea.height());
-                next = NULL;
+                next = nullptr;
                 foreach (EffectWindow * e, m_motionManager.managedWindows()) {
                     DataHash::const_iterator winData = m_windowData.find(e);
                     if (winData == m_windowData.end() || !winData->visible)
                         continue;
                     QRectF eArea = m_motionManager.transformedGeometry(e);
                     if (eArea.intersects(detectRect) &&
                             eArea.x() + eArea.width() < wArea.x() + wArea.width()) {
-                        if (next == NULL)
+                        if (next == nullptr)
                             next = e;
                         else {
                             QRectF nArea = m_motionManager.transformedGeometry(next);
                             if (eArea.x() + eArea.width() > nArea.x() + nArea.width())
                                 next = e;
                         }
                     }
                 }
-                if (next == NULL) {
+                if (next == nullptr) {
                     if (wrap)   // We are at the left-most window, now get the right-most one to wrap
                         return relativeWindow(w, 1000, 0, false);
                     break; // No more windows to the left
@@ -1870,24 +1870,24 @@
             for (int i = 0; i < ydiff; i++) {
                 QRectF wArea = m_motionManager.transformedGeometry(w);
                 detectRect = QRect(wArea.x(), 0, wArea.width(), area.height());
-                next = NULL;
+                next = nullptr;
                 foreach (EffectWindow * e, m_motionManager.managedWindows()) {
                     DataHash::const_iterator winData = m_windowData.find(e);
                     if (winData == m_windowData.end() || !winData->visible)
                         continue;
                     QRectF eArea = m_motionManager.transformedGeometry(e);
                     if (eArea.intersects(detectRect) &&
                             eArea.y() > wArea.y()) {
-                        if (next == NULL)
+                        if (next == nullptr)
                             next = e;
                         else {
                             QRectF nArea = m_motionManager.transformedGeometry(next);
                             if (eArea.y() < nArea.y())
                                 next = e;
                         }
                     }
                 }
-                if (next == NULL) {
+                if (next == nullptr) {
                     if (wrap)   // We are at the bottom-most window, now get the top-most one to wrap
                         return relativeWindow(w, 0, -1000, false);
                     break; // No more windows to the bottom
@@ -1900,24 +1900,24 @@
             for (int i = 0; i < -ydiff; i++) {
                 QRectF wArea = m_motionManager.transformedGeometry(w);
                 detectRect = QRect(wArea.x(), 0, wArea.width(), area.height());
-                next = NULL;
+                next = nullptr;
                 foreach (EffectWindow * e, m_motionManager.managedWindows()) {
                     DataHash::const_iterator winData = m_windowData.find(e);
                     if (winData == m_windowData.end() || !winData->visible)
                         continue;
                     QRectF eArea = m_motionManager.transformedGeometry(e);
                     if (eArea.intersects(detectRect) &&
                             eArea.y() + eArea.height() < wArea.y() + wArea.height()) {
-                        if (next == NULL)
+                        if (next == nullptr)
                             next = e;
                         else {
                             QRectF nArea = m_motionManager.transformedGeometry(next);
                             if (eArea.y() + eArea.height() > nArea.y() + nArea.height())
                                 next = e;
                         }
                     }
                 }
-                if (next == NULL) {
+                if (next == nullptr) {
                     if (wrap)   // We are at the top-most window, now get the bottom-most one to wrap
                         return relativeWindow(w, 0, 1000, false);
                     break; // No more windows to the top
@@ -1933,7 +1933,7 @@
 
 EffectWindow* PresentWindowsEffect::findFirstWindow() const
 {
-    EffectWindow *topLeft = NULL;
+    EffectWindow *topLeft = nullptr;
     QRectF topLeftGeometry;
     foreach (EffectWindow * w, m_motionManager.managedWindows()) {
         DataHash::const_iterator winData = m_windowData.find(w);
@@ -1944,7 +1944,7 @@
             continue; // Not visible
         if (winData->deleted)
             continue; // Window has been closed
-        if (topLeft == NULL) {
+        if (topLeft == nullptr) {
             topLeft = w;
             topLeftGeometry = geometry;
         } else if (geometry.x() < topLeftGeometry.x() || geometry.y() < topLeftGeometry.y()) {
diff --git a/effects/presentwindows/presentwindows_config.h b/effects/presentwindows/presentwindows_config.h
--- a/effects/presentwindows/presentwindows_config.h
+++ b/effects/presentwindows/presentwindows_config.h
@@ -40,7 +40,7 @@
 {
     Q_OBJECT
 public:
-    explicit PresentWindowsEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit PresentWindowsEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~PresentWindowsEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/resize/resize.cpp b/effects/resize/resize.cpp
--- a/effects/resize/resize.cpp
+++ b/effects/resize/resize.cpp
@@ -38,7 +38,7 @@
 ResizeEffect::ResizeEffect()
     : AnimationEffect()
     , m_active(false)
-    , m_resizeWindow(0)
+    , m_resizeWindow(nullptr)
 {
     initConfig<ResizeConfig>();
     reconfigure(ReconfigureAll);
@@ -102,7 +102,7 @@
                     verts << r.x() + r.width() << r.y() + r.height();
                     verts << r.x() + r.width() << r.y();
                 }
-                vbo->setData(verts.count() / 2, 2, verts.data(), NULL);
+                vbo->setData(verts.count() / 2, 2, verts.data(), nullptr);
                 vbo->render(GL_TRIANGLES);
                 glDisable(GL_BLEND);
             }
@@ -159,7 +159,7 @@
 {
     if (m_active && w == m_resizeWindow) {
         m_active = false;
-        m_resizeWindow = NULL;
+        m_resizeWindow = nullptr;
         if (m_features & TextureScale)
             animate(w, CrossFadePrevious, 0, 150, FPx2(1.0));
         effects->addRepaintFull();
diff --git a/effects/resize/resize_config.h b/effects/resize/resize_config.h
--- a/effects/resize/resize_config.h
+++ b/effects/resize/resize_config.h
@@ -33,14 +33,14 @@
 {
     Q_OBJECT
 public:
-    explicit ResizeEffectConfigForm(QWidget* parent = 0);
+    explicit ResizeEffectConfigForm(QWidget* parent = nullptr);
 };
 
 class ResizeEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit ResizeEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit ResizeEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
 
 public Q_SLOTS:
     void save() override;
diff --git a/effects/screenedge/screenedgeeffect.cpp b/effects/screenedge/screenedgeeffect.cpp
--- a/effects/screenedge/screenedgeeffect.cpp
+++ b/effects/screenedge/screenedgeeffect.cpp
@@ -233,7 +233,7 @@
         }
         if (glow->texture.isNull()) {
             delete glow;
-            return NULL;
+            return nullptr;
         }
     } else if (effects->compositingType() == XRenderCompositing) {
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
@@ -246,7 +246,7 @@
         }
         if (glow->picture.isNull()) {
             delete glow;
-            return NULL;
+            return nullptr;
         }
 #endif
     } else if (effects->compositingType() == QPainterCompositing) {
@@ -259,7 +259,7 @@
         }
         if (glow->image.isNull()) {
             delete glow;
-            return NULL;
+            return nullptr;
         }
     }
 
@@ -281,7 +281,7 @@
     case ElectricBottomLeft:
         return new T(m_glow->pixmap(QStringLiteral("topright")).toImage());
     default:
-        return NULL;
+        return nullptr;
     }
 }
 
@@ -336,7 +336,7 @@
         pixmapPosition = QPoint(size.width() - c.width(), 0);
         break;
     default:
-        return NULL;
+        return nullptr;
     }
     QPixmap image(size);
     image.fill(Qt::transparent);
diff --git a/effects/screenshot/screenshot.cpp b/effects/screenshot/screenshot.cpp
--- a/effects/screenshot/screenshot.cpp
+++ b/effects/screenshot/screenshot.cpp
@@ -58,7 +58,7 @@
 }
 
 ScreenShotEffect::ScreenShotEffect()
-    : m_scheduledScreenshot(0)
+    : m_scheduledScreenshot(nullptr)
 {
     connect(effects, &EffectsHandler::windowClosed, this, &ScreenShotEffect::windowClosed);
     QDBusConnection::sessionBus().registerObject(QStringLiteral("/Screenshot"), this, QDBusConnection::ExportScriptableContents);
@@ -234,7 +234,7 @@
                 ScreenShotEffect::convertFromGLImage(img, width, height);
             }
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
-            xcb_image_t *xImage = NULL;
+            xcb_image_t *xImage = nullptr;
             if (effects->compositingType() == XRenderCompositing) {
                 setXRenderOffscreen(true);
                 effects->drawWindow(m_scheduledScreenshot, mask, QRegion(0, 0, width, height), d);
@@ -276,7 +276,7 @@
             }
 #endif
         }
-        m_scheduledScreenshot = NULL;
+        m_scheduledScreenshot = nullptr;
     }
 
     if (!m_scheduledGeometry.isNull()) {
@@ -373,7 +373,7 @@
             !m_scheduledScreenshot->isMinimized() && !m_scheduledScreenshot->isDeleted() &&
             m_scheduledScreenshot->geometry().contains(cursor))
             break;
-        m_scheduledScreenshot = 0;
+        m_scheduledScreenshot = nullptr;
     }
     if (m_scheduledScreenshot) {
         m_windowMode = WindowMode::Xpixmap;
@@ -626,7 +626,7 @@
 
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
     if (effects->compositingType() == XRenderCompositing) {
-    xcb_image_t *xImage = NULL;
+    xcb_image_t *xImage = nullptr;
         img = xPictureToImage(effects->xrenderBufferPicture(), geometry, &xImage);
         if (xImage) {
             xcb_image_destroy(xImage);
@@ -684,13 +684,13 @@
 
 bool ScreenShotEffect::isActive() const
 {
-    return (m_scheduledScreenshot != NULL || !m_scheduledGeometry.isNull()) && !effects->isScreenLocked();
+    return (m_scheduledScreenshot != nullptr || !m_scheduledGeometry.isNull()) && !effects->isScreenLocked();
 }
 
 void ScreenShotEffect::windowClosed( EffectWindow* w )
 {
     if (w == m_scheduledScreenshot) {
-        m_scheduledScreenshot = NULL;
+        m_scheduledScreenshot = nullptr;
         screenshotWindowUnderCursor(m_type);
     }
 }
diff --git a/effects/showfps/showfps.cpp b/effects/showfps/showfps.cpp
--- a/effects/showfps/showfps.cpp
+++ b/effects/showfps/showfps.cpp
@@ -201,7 +201,7 @@
     verts << x << y + MAX_TIME;
     verts << x + 2 * NUM_PAINTS + FPS_WIDTH << y + MAX_TIME;
     verts << x + 2 * NUM_PAINTS + FPS_WIDTH << y;
-    vbo->setData(6, 2, verts.constData(), NULL);
+    vbo->setData(6, 2, verts.constData(), nullptr);
     vbo->render(GL_TRIANGLES);
     y += MAX_TIME; // paint up from the bottom
     color.setRed(0);
@@ -214,7 +214,7 @@
     verts << x << y;
     verts << x + FPS_WIDTH << y;
     verts << x + FPS_WIDTH << y - fps;
-    vbo->setData(6, 2, verts.constData(), NULL);
+    vbo->setData(6, 2, verts.constData(), nullptr);
     vbo->render(GL_TRIANGLES);
 
 
@@ -227,7 +227,7 @@
         vertices << x << y - i;
         vertices << x + FPS_WIDTH << y - i;
     }
-    vbo->setData(vertices.size() / 2, 2, vertices.constData(), NULL);
+    vbo->setData(vertices.size() / 2, 2, vertices.constData(), nullptr);
     vbo->render(GL_LINES);
     x += FPS_WIDTH;
 
@@ -406,16 +406,16 @@
             verts << x << y - h;
             verts << x + values.count() << y - h;
         }
-        vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+        vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
         vbo->render(GL_LINES);
         // Then the graph values
         int lastValue = 0;
         verts.clear();
         for (int i = 0; i < values.count(); i++) {
             int value = values[ i ];
             if (colorize && value != lastValue) {
                 if (!verts.isEmpty()) {
-                    vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+                    vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
                     vbo->render(GL_LINES);
                 }
                 verts.clear();
@@ -435,7 +435,7 @@
             lastValue = value;
         }
         if (!verts.isEmpty()) {
-            vbo->setData(verts.size() / 2, 2, verts.constData(), NULL);
+            vbo->setData(verts.size() / 2, 2, verts.constData(), nullptr);
             vbo->render(GL_LINES);
         }
     }
diff --git a/effects/showfps/showfps_config.h b/effects/showfps/showfps_config.h
--- a/effects/showfps/showfps_config.h
+++ b/effects/showfps/showfps_config.h
@@ -32,7 +32,7 @@
 {
     Q_OBJECT
 public:
-    explicit ShowFpsEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit ShowFpsEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~ShowFpsEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/slideback/slideback.cpp b/effects/slideback/slideback.cpp
--- a/effects/slideback/slideback.cpp
+++ b/effects/slideback/slideback.cpp
@@ -26,7 +26,7 @@
 SlideBackEffect::SlideBackEffect()
 {
     m_tabboxActive = 0;
-    m_justMapped = m_upmostWindow = NULL;
+    m_justMapped = m_upmostWindow = nullptr;
     connect(effects, &EffectsHandler::windowAdded, this, &SlideBackEffect::slotWindowAdded);
     connect(effects, &EffectsHandler::windowDeleted, this, &SlideBackEffect::slotWindowDeleted);
     connect(effects, &EffectsHandler::windowUnminimized, this, &SlideBackEffect::slotWindowUnminimized);
@@ -54,7 +54,7 @@
     m_upmostWindow = usableNewStackingOrder.last();
 
     if (m_upmostWindow == m_justMapped ) // a window was added, got on top, stacking changed. Nothing impressive
-        m_justMapped = 0;
+        m_justMapped = nullptr;
     else if (!usableOldStackingOrder.isEmpty() && m_upmostWindow != usableOldStackingOrder.last())
         windowRaised(m_upmostWindow);
 
@@ -259,9 +259,9 @@
 void SlideBackEffect::slotWindowDeleted(EffectWindow* w)
 {
     if (w == m_upmostWindow)
-        m_upmostWindow = 0;
+        m_upmostWindow = nullptr;
     if (w == m_justMapped)
-        m_justMapped = 0;
+        m_justMapped = nullptr;
     usableOldStackingOrder.removeAll(w);
     oldStackingOrder.removeAll(w);
     coveringWindows.removeAll(w);
diff --git a/effects/startupfeedback/startupfeedback.cpp b/effects/startupfeedback/startupfeedback.cpp
--- a/effects/startupfeedback/startupfeedback.cpp
+++ b/effects/startupfeedback/startupfeedback.cpp
@@ -78,13 +78,13 @@
     , m_active(false)
     , m_frame(0)
     , m_progress(0)
-    , m_texture(0)
+    , m_texture(nullptr)
     , m_type(BouncingFeedback)
-    , m_blinkingShader(0)
+    , m_blinkingShader(nullptr)
     , m_cursorSize(0)
 {
     for (int i = 0; i < 5; ++i) {
-        m_bouncingTextures[i] = 0;
+        m_bouncingTextures[i] = nullptr;
     }
     if (KWindowSystem::isPlatformX11()) {
         m_selection = new KSelectionOwner("_KDE_STARTUP_FEEDBACK", xcbConnection(), x11RootWindow(), this);
@@ -276,7 +276,7 @@
     if (m_type == BouncingFeedback)
         m_bounceSizesRatio = IconSize(KIconLoader::Small) / 16.0;
     QPixmap iconPixmap = KIconLoader::global()->loadIcon(icon, KIconLoader::Small, 0,
-                         KIconLoader::DefaultState, QStringList(), 0, true);  // return null pixmap if not found
+                         KIconLoader::DefaultState, QStringList(), nullptr, true);  // return null pixmap if not found
     if (iconPixmap.isNull())
         iconPixmap = SmallIcon(QStringLiteral("system-run"));
     prepareTextures(iconPixmap);
@@ -307,13 +307,13 @@
     case BouncingFeedback:
         for (int i = 0; i < 5; ++i) {
             delete m_bouncingTextures[i];
-            m_bouncingTextures[i] = 0;
+            m_bouncingTextures[i] = nullptr;
         }
         break;
     case BlinkingFeedback:
     case PassiveFeedback:
         delete m_texture;
-        m_texture = 0;
+        m_texture = nullptr;
         break;
     case NoFeedback:
         return; // don't want the full repaint
@@ -371,7 +371,7 @@
     else
         xDiff = 32 + 7;
     int yDiff = xDiff;
-    GLTexture* texture = 0;
+    GLTexture* texture = nullptr;
     int yOffset = 0;
     switch(m_type) {
     case BouncingFeedback:
diff --git a/effects/thumbnailaside/thumbnailaside.cpp b/effects/thumbnailaside/thumbnailaside.cpp
--- a/effects/thumbnailaside/thumbnailaside.cpp
+++ b/effects/thumbnailaside/thumbnailaside.cpp
@@ -113,7 +113,7 @@
 void ThumbnailAsideEffect::toggleCurrentThumbnail()
 {
     EffectWindow* active = effects->activeWindow();
-    if (active == NULL)
+    if (active == nullptr)
         return;
     if (windows.contains(active))
         removeThumbnail(active);
diff --git a/effects/thumbnailaside/thumbnailaside_config.h b/effects/thumbnailaside/thumbnailaside_config.h
--- a/effects/thumbnailaside/thumbnailaside_config.h
+++ b/effects/thumbnailaside/thumbnailaside_config.h
@@ -41,7 +41,7 @@
 {
     Q_OBJECT
 public:
-    explicit ThumbnailAsideEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit ThumbnailAsideEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~ThumbnailAsideEffectConfig() override;
 
     void save() override;
diff --git a/effects/touchpoints/touchpoints.cpp b/effects/touchpoints/touchpoints.cpp
--- a/effects/touchpoints/touchpoints.cpp
+++ b/effects/touchpoints/touchpoints.cpp
@@ -231,7 +231,7 @@
         x = c * x - s * y;
         y = s * t + c * y;
     }
-    vbo->setData(verts.size() / 2, 2, verts.data(), NULL);
+    vbo->setData(verts.size() / 2, 2, verts.data(), nullptr);
     vbo->render(GL_LINE_LOOP);
 }
 
diff --git a/effects/trackmouse/trackmouse.cpp b/effects/trackmouse/trackmouse.cpp
--- a/effects/trackmouse/trackmouse.cpp
+++ b/effects/trackmouse/trackmouse.cpp
@@ -46,9 +46,9 @@
     : m_angle(0)
 {
     initConfig<TrackMouseConfig>();
-    m_texture[0] = m_texture[1] = 0;
+    m_texture[0] = m_texture[1] = nullptr;
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
-    m_picture[0] = m_picture[1] = 0;
+    m_picture[0] = m_picture[1] = nullptr;
     if ( effects->compositingType() == XRenderCompositing)
         m_angleBase = 1.57079632679489661923; // Pi/2
 #endif
@@ -74,16 +74,16 @@
     if (m_mousePolling)
         effects->stopMousePolling();
     for (int i = 0; i < 2; ++i) {
-        delete m_texture[i]; m_texture[i] = 0;
+        delete m_texture[i]; m_texture[i] = nullptr;
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
-        delete m_picture[i]; m_picture[i] = 0;
+        delete m_picture[i]; m_picture[i] = nullptr;
 #endif
     }
 }
 
 void TrackMouseEffect::reconfigure(ReconfigureFlags)
 {
-    m_modifiers = 0;
+    m_modifiers = nullptr;
     TrackMouseConfig::self()->read();
     if (TrackMouseConfig::shift())
         m_modifiers |= Qt::ShiftModifier;
@@ -161,7 +161,7 @@
             };
 #undef DOUBLE_TO_FIXED
             xcb_render_set_picture_transform(xcbConnection(), picture, xform);
-            xcb_render_set_picture_filter(xcbConnection(), picture, 8, "bilinear", 0, NULL);
+            xcb_render_set_picture_filter(xcbConnection(), picture, 8, "bilinear", 0, nullptr);
             const QRect &rect = m_lastRect[i];
             xcb_render_composite(xcbConnection(), XCB_RENDER_PICT_OP_OVER, picture, XCB_RENDER_PICTURE_NONE,
                                  effects->xrenderBufferPicture(), 0, 0, 0, 0,
diff --git a/effects/trackmouse/trackmouse_config.h b/effects/trackmouse/trackmouse_config.h
--- a/effects/trackmouse/trackmouse_config.h
+++ b/effects/trackmouse/trackmouse_config.h
@@ -42,7 +42,7 @@
 {
     Q_OBJECT
 public:
-    explicit TrackMouseEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit TrackMouseEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~TrackMouseEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/windowgeometry/windowgeometry.cpp b/effects/windowgeometry/windowgeometry.cpp
--- a/effects/windowgeometry/windowgeometry.cpp
+++ b/effects/windowgeometry/windowgeometry.cpp
@@ -37,7 +37,7 @@
     initConfig<WindowGeometryConfiguration>();
     iAmActivated = true;
     iAmActive = false;
-    myResizeWindow = 0L;
+    myResizeWindow = nullptr;
 #define myResizeString "Window geometry display, %1 and %2 are the new size," \
                        " %3 and %4 are pixel increments - avoid reformatting or suffixes like 'px'", \
                        "Width: %1 (%3)\nHeight: %2 (%4)"
@@ -128,7 +128,7 @@
 {
     if (iAmActive && w == myResizeWindow) {
         iAmActive = false;
-        myResizeWindow = 0L;
+        myResizeWindow = nullptr;
         w->addRepaintFull();
         if (myExtraDirtyArea.isValid())
             w->addLayerRepaint(myExtraDirtyArea);
diff --git a/effects/windowgeometry/windowgeometry_config.h b/effects/windowgeometry/windowgeometry_config.h
--- a/effects/windowgeometry/windowgeometry_config.h
+++ b/effects/windowgeometry/windowgeometry_config.h
@@ -40,7 +40,7 @@
 {
     Q_OBJECT
 public:
-    explicit WindowGeometryConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit WindowGeometryConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~WindowGeometryConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/wobblywindows/wobblywindows_config.h b/effects/wobblywindows/wobblywindows_config.h
--- a/effects/wobblywindows/wobblywindows_config.h
+++ b/effects/wobblywindows/wobblywindows_config.h
@@ -34,7 +34,7 @@
 {
     Q_OBJECT
 public:
-    explicit WobblyWindowsEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit WobblyWindowsEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~WobblyWindowsEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/effects/zoom/zoom.cpp b/effects/zoom/zoom.cpp
--- a/effects/zoom/zoom.cpp
+++ b/effects/zoom/zoom.cpp
@@ -61,7 +61,7 @@
     , moveFactor(20.0)
 {
     initConfig<ZoomConfig>();
-    QAction* a = 0;
+    QAction* a = nullptr;
     a = KStandardAction::zoomIn(this, SLOT(zoomIn()), this);
     KGlobalAccel::self()->setDefaultShortcut(a, QList<QKeySequence>() << Qt::META + Qt::Key_Equal);
     KGlobalAccel::self()->setShortcut(a, QList<QKeySequence>() << Qt::META + Qt::Key_Equal);
@@ -369,7 +369,7 @@
                 DOUBLE_TO_FIXED(0), DOUBLE_TO_FIXED(0), DOUBLE_TO_FIXED(1)
             };
             if (mousePointer == MousePointerScale) {
-                xcb_render_set_picture_filter(xcbConnection(), *xrenderPicture, 4, const_cast<char*>("good"), 0, NULL);
+                xcb_render_set_picture_filter(xcbConnection(), *xrenderPicture, 4, const_cast<char*>("good"), 0, nullptr);
                 const xcb_render_transform_t xform = {
                     DOUBLE_TO_FIXED(1.0 / zoom), DOUBLE_TO_FIXED(0), DOUBLE_TO_FIXED(0),
                     DOUBLE_TO_FIXED(0), DOUBLE_TO_FIXED(1.0 / zoom), DOUBLE_TO_FIXED(0),
diff --git a/effects/zoom/zoom_config.h b/effects/zoom/zoom_config.h
--- a/effects/zoom/zoom_config.h
+++ b/effects/zoom/zoom_config.h
@@ -34,14 +34,14 @@
 {
     Q_OBJECT
 public:
-    explicit ZoomEffectConfigForm(QWidget* parent = 0);
+    explicit ZoomEffectConfigForm(QWidget* parent = nullptr);
 };
 
 class ZoomEffectConfig : public KCModule
 {
     Q_OBJECT
 public:
-    explicit ZoomEffectConfig(QWidget* parent = 0, const QVariantList& args = QVariantList());
+    explicit ZoomEffectConfig(QWidget* parent = nullptr, const QVariantList& args = QVariantList());
     ~ZoomEffectConfig() override;
 
 public Q_SLOTS:
diff --git a/events.cpp b/events.cpp
--- a/events.cpp
+++ b/events.cpp
@@ -326,7 +326,7 @@
         const auto *event = reinterpret_cast<xcb_map_notify_event_t*>(e);
         if (event->override_redirect) {
             Unmanaged* c = findUnmanaged(event->window);
-            if (c == NULL)
+            if (c == nullptr)
                 c = createUnmanaged(event->window);
             if (c)
                 return c->windowEvent(e);
@@ -373,9 +373,9 @@
             if (!currentInput.isNull() && (currentInput->focus == XCB_WINDOW_NONE || currentInput->focus == XCB_INPUT_FOCUS_POINTER_ROOT || lostFocusPointerToRoot)) {
                 //kWarning( 1212 ) << "X focus set to None/PointerRoot, reseting focus" ;
                 AbstractClient *c = mostRecentlyActivatedClient();
-                if (c != NULL)
+                if (c != nullptr)
                     requestFocus(c, true);
-                else if (activateNextClient(NULL))
+                else if (activateNextClient(nullptr))
                     ; // ok, activated
                 else
                     focusToNull();
@@ -444,7 +444,7 @@
                 emit opacityChanged(this, old_opacity);
             } else {
                 // forward to the frame if there's possibly another compositing manager running
-                NETWinInfo i(connection(), frameId(), rootWindow(), 0, 0);
+                NETWinInfo i(connection(), frameId(), rootWindow(), nullptr, nullptr);
                 i.setOpacity(info->opacity());
             }
         }
@@ -821,7 +821,7 @@
             }
         }
         if (options->focusPolicy() == Options::FocusStrictlyUnderMouse && isActive() && lostMouse) {
-            workspace()->requestDelayFocus(0);
+            workspace()->requestDelayFocus(nullptr);
         }
         return;
     }
diff --git a/focuschain.cpp b/focuschain.cpp
--- a/focuschain.cpp
+++ b/focuschain.cpp
@@ -29,14 +29,14 @@
 FocusChain::FocusChain(QObject *parent)
     : QObject(parent)
     , m_separateScreenFocus(false)
-    , m_activeClient(NULL)
+    , m_activeClient(nullptr)
     , m_currentDesktop(0)
 {
 }
 
 FocusChain::~FocusChain()
 {
-    s_manager = NULL;
+    s_manager = nullptr;
 }
 
 void FocusChain::remove(AbstractClient *client)
@@ -68,7 +68,7 @@
 {
     auto it = m_desktopFocusChains.constFind(desktop);
     if (it == m_desktopFocusChains.constEnd()) {
-        return NULL;
+        return nullptr;
     }
     const auto &chain = it.value();
     for (int i = chain.size() - 1; i >= 0; --i) {
@@ -79,7 +79,7 @@
             return tmp;
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 void FocusChain::update(AbstractClient *client, FocusChain::Change change)
@@ -191,15 +191,15 @@
 AbstractClient *FocusChain::firstMostRecentlyUsed() const
 {
     if (m_mostRecentlyUsed.isEmpty()) {
-        return NULL;
+        return nullptr;
     }
     return m_mostRecentlyUsed.first();
 }
 
 AbstractClient *FocusChain::nextMostRecentlyUsed(AbstractClient *reference) const
 {
     if (m_mostRecentlyUsed.isEmpty()) {
-        return NULL;
+        return nullptr;
     }
     const int index = m_mostRecentlyUsed.indexOf(reference);
     if (index == -1) {
@@ -223,16 +223,16 @@
 {
     auto it = m_desktopFocusChains.constFind(desktop);
     if (it == m_desktopFocusChains.constEnd()) {
-        return NULL;
+        return nullptr;
     }
     const auto &chain = it.value();
     for (int i = chain.size() - 1; i >= 0; --i) {
         auto client = chain.at(i);
         if (isUsableFocusCandidate(client, reference)) {
             return client;
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 void FocusChain::makeFirstInChain(AbstractClient *client, Chain &chain)
diff --git a/geometry.cpp b/geometry.cpp
--- a/geometry.cpp
+++ b/geometry.cpp
@@ -896,7 +896,7 @@
 // (the property with the size of the frame remains on the window after the crash).
 void Workspace::fixPositionAfterCrash(xcb_window_t w, const xcb_get_geometry_reply_t *geometry)
 {
-    NETWinInfo i(connection(), w, rootWindow(), NET::WMFrameExtents, 0);
+    NETWinInfo i(connection(), w, rootWindow(), NET::WMFrameExtents, nullptr);
     NETStrut frame = i.frameExtents();
 
     if (frame.left != 0 || frame.top != 0) {
@@ -2179,7 +2179,7 @@
             m_client->tabGroup()->blockStateUpdates(false);
             m_client->tabGroup()->updateStates(dynamic_cast<Client*>(m_client), m_states);
         }
-        m_client = 0;
+        m_client = nullptr;
     }
 private:
     AbstractClient *m_client;
@@ -2551,7 +2551,7 @@
     return total;
 }
 
-static GeometryTip* geometryTip    = 0;
+static GeometryTip* geometryTip    = nullptr;
 
 void Client::positionGeometryTip()
 {
@@ -2578,10 +2578,10 @@
 bool AbstractClient::startMoveResize()
 {
     Q_ASSERT(!isMoveResize());
-    Q_ASSERT(QWidget::keyboardGrabber() == NULL);
-    Q_ASSERT(QWidget::mouseGrabber() == NULL);
+    Q_ASSERT(QWidget::keyboardGrabber() == nullptr);
+    Q_ASSERT(QWidget::mouseGrabber() == nullptr);
     stopDelayedMoveResize();
-    if (QApplication::activePopupWidget() != NULL)
+    if (QApplication::activePopupWidget() != nullptr)
         return false; // popups have grab
     if (isFullScreen() && (screens()->count() < 2 || !isMovableAcrossScreens()))
         return false;
@@ -2625,15 +2625,15 @@
     // something with Enter/LeaveNotify events, looks like XFree performance problem or something *shrug*
     // (https://lists.kde.org/?t=107302193400001&r=1&w=2)
     QRect r = workspace()->clientArea(FullArea, this);
-    m_moveResizeGrabWindow.create(r, XCB_WINDOW_CLASS_INPUT_ONLY, 0, NULL, rootWindow());
+    m_moveResizeGrabWindow.create(r, XCB_WINDOW_CLASS_INPUT_ONLY, 0, nullptr, rootWindow());
     m_moveResizeGrabWindow.map();
     m_moveResizeGrabWindow.raise();
     updateXTime();
     const xcb_grab_pointer_cookie_t cookie = xcb_grab_pointer_unchecked(connection(), false, m_moveResizeGrabWindow,
         XCB_EVENT_MASK_BUTTON_PRESS | XCB_EVENT_MASK_BUTTON_RELEASE | XCB_EVENT_MASK_POINTER_MOTION |
         XCB_EVENT_MASK_ENTER_WINDOW | XCB_EVENT_MASK_LEAVE_WINDOW,
         XCB_GRAB_MODE_ASYNC, XCB_GRAB_MODE_ASYNC, m_moveResizeGrabWindow, Cursor::x11Cursor(cursor()), xTime());
-    ScopedCPointer<xcb_grab_pointer_reply_t> pointerGrab(xcb_grab_pointer_reply(connection(), cookie, NULL));
+    ScopedCPointer<xcb_grab_pointer_reply_t> pointerGrab(xcb_grab_pointer_reply(connection(), cookie, nullptr));
     if (!pointerGrab.isNull() && pointerGrab->status == XCB_GRAB_STATUS_SUCCESS) {
         has_grab = true;
     }
@@ -2706,7 +2706,7 @@
     if (geometryTip) {
         geometryTip->hide();
         delete geometryTip;
-        geometryTip = NULL;
+        geometryTip = nullptr;
     }
     if (move_resize_has_keyboard_grab)
         ungrabXKeyboard();
@@ -2716,7 +2716,7 @@
     if (syncRequest.counter == XCB_NONE) // don't forget to sanitize since the timeout will no more fire
         syncRequest.isPending = false;
     delete syncRequest.timeout;
-    syncRequest.timeout = NULL;
+    syncRequest.timeout = nullptr;
     AbstractClient::leaveMoveResize();
 }
 
diff --git a/geometrytip.cpp b/geometrytip.cpp
--- a/geometrytip.cpp
+++ b/geometrytip.cpp
@@ -24,7 +24,7 @@
 {
 
 GeometryTip::GeometryTip(const Xcb::GeometryHints* xSizeHints):
-    QLabel(0)
+    QLabel(nullptr)
 {
     setObjectName(QLatin1String("kwingeometry"));
     setMargin(1);
diff --git a/group.cpp b/group.cpp
--- a/group.cpp
+++ b/group.cpp
@@ -54,9 +54,9 @@
 //********************************************
 
 Group::Group(Window leader_P)
-    :   leader_client(NULL),
+    :   leader_client(nullptr),
         leader_wid(leader_P),
-        leader_info(NULL),
+        leader_info(nullptr),
         user_time(-1U),
         refcount(0)
 {
@@ -77,7 +77,7 @@
 
 QIcon Group::icon() const
 {
-    if (leader_client != NULL)
+    if (leader_client != nullptr)
         return leader_client->icon();
     else if (leader_wid != None) {
         QIcon ic;
@@ -143,7 +143,7 @@
 void Group::lostLeader()
 {
     Q_ASSERT(!_members.contains(leader_client));
-    leader_client = NULL;
+    leader_client = nullptr;
     if (_members.isEmpty()) {
         workspace()->removeGroup(this);
         delete this;
@@ -162,21 +162,21 @@
             ++it)
         if ((*it)->leader() == leader)
             return *it;
-    return NULL;
+    return nullptr;
 }
 
 // Client is group transient, but has no group set. Try to find
 // group with windows with the same client leader.
 Group* Workspace::findClientLeaderGroup(const Client* c) const
 {
-    Group* ret = NULL;
+    Group* ret = nullptr;
     for (ClientList::ConstIterator it = clients.constBegin();
             it != clients.constEnd();
             ++it) {
         if (*it == c)
             continue;
         if ((*it)->wmClientLeader() == c->wmClientLeader()) {
-            if (ret == NULL || ret == (*it)->group())
+            if (ret == nullptr || ret == (*it)->group())
                 ret = (*it)->group();
             else {
                 // There are already two groups with the same client leader.
@@ -439,11 +439,11 @@
         m_transientForId = new_transient_for_id;
         if (m_transientForId != XCB_WINDOW_NONE && !groupTransient()) {
             transient_for = workspace()->findClient(Predicate::WindowMatch, m_transientForId);
-            Q_ASSERT(transient_for != NULL);   // verifyTransient() had to check this
+            Q_ASSERT(transient_for != nullptr);   // verifyTransient() had to check this
             transient_for->addTransient(this);
         } // checkGroup() will check 'check_active_modal'
         setTransientFor(transient_for);
-        checkGroup(NULL, true);   // force, because transiency has changed
+        checkGroup(nullptr, true);   // force, because transiency has changed
         workspace()->updateClientLayer(this);
         workspace()->resetUpdateToolWindowsTimer();
         emit transientChanged();
@@ -516,7 +516,7 @@
     // added 'this' to those transient lists :(
     ClientList group_members = group()->members();
     group()->removeMember(this);
-    in_group = NULL;
+    in_group = nullptr;
     for (ClientList::ConstIterator it = group_members.constBegin();
             it != group_members.constEnd();
             ++it)
@@ -547,7 +547,7 @@
             if (*it1 == *it2)
                 continue;
             for (AbstractClient* cl = (*it2)->transientFor();
-                    cl != NULL;
+                    cl != nullptr;
                     cl = cl->transientFor()) {
                 if (cl == *it1) {
                     // don't use removeTransient(), that would modify *it2 too
@@ -631,16 +631,16 @@
     xcb_window_t loop_pos = new_transient_for;
     while (loop_pos != XCB_WINDOW_NONE && loop_pos != rootWindow()) {
         Client* pos = workspace()->findClient(Predicate::WindowMatch, loop_pos);
-        if (pos == NULL)
+        if (pos == nullptr)
             break;
         loop_pos = pos->m_transientForId;
         if (--count == 0 || pos == this) {
             qCWarning(KWIN_CORE) << "Client " << this << " caused WM_TRANSIENT_FOR loop." ;
             new_transient_for = rootWindow();
         }
     }
     if (new_transient_for != rootWindow()
-            && workspace()->findClient(Predicate::WindowMatch, new_transient_for) == NULL) {
+            && workspace()->findClient(Predicate::WindowMatch, new_transient_for) == nullptr) {
         // it's transient for a specific window, but that window is not mapped
         new_transient_for = rootWindow();
     }
@@ -762,36 +762,36 @@
             return ret;
     if (isModal() && allow_itself)
         return this;
-    return NULL;
+    return nullptr;
 }
 
 // Client::window_group only holds the contents of the hint,
 // but it should be used only to find the group, not for anything else
 // Argument is only when some specific group needs to be set.
 void Client::checkGroup(Group* set_group, bool force)
 {
     Group* old_group = in_group;
-    if (old_group != NULL)
+    if (old_group != nullptr)
         old_group->ref(); // turn off automatic deleting
-    if (set_group != NULL) {
+    if (set_group != nullptr) {
         if (set_group != in_group) {
-            if (in_group != NULL)
+            if (in_group != nullptr)
                 in_group->removeMember(this);
             in_group = set_group;
             in_group->addMember(this);
         }
     } else if (info->groupLeader() != XCB_WINDOW_NONE) {
         Group* new_group = workspace()->findGroup(info->groupLeader());
         Client *t = qobject_cast<Client*>(transientFor());
-        if (t != NULL && t->group() != new_group) {
+        if (t != nullptr && t->group() != new_group) {
             // move the window to the right group (e.g. a dialog provided
             // by different app, but transient for this one, so make it part of that group)
             new_group = t->group();
         }
-        if (new_group == NULL)   // doesn't exist yet
+        if (new_group == nullptr)   // doesn't exist yet
             new_group = new Group(info->groupLeader());
         if (new_group != in_group) {
-            if (in_group != NULL)
+            if (in_group != nullptr)
                 in_group->removeMember(this);
             in_group = new_group;
             in_group->addMember(this);
@@ -802,19 +802,19 @@
             // so make it part of that group
             Group* new_group = t->group();
             if (new_group != in_group) {
-                if (in_group != NULL)
+                if (in_group != nullptr)
                     in_group->removeMember(this);
                 in_group = t->group();
                 in_group->addMember(this);
             }
         } else if (groupTransient()) {
             // group transient which actually doesn't have a group :(
             // try creating group with other windows with the same client leader
             Group* new_group = workspace()->findClientLeaderGroup(this);
-            if (new_group == NULL)
+            if (new_group == nullptr)
                 new_group = new Group(None);
             if (new_group != in_group) {
-                if (in_group != NULL)
+                if (in_group != nullptr)
                     in_group->removeMember(this);
                 in_group = new_group;
                 in_group->addMember(this);
@@ -824,11 +824,11 @@
             // or minimizing together the whole group, but as long as it is used
             // only for dialogs it's better to keep windows from one app in one group.
             Group* new_group = workspace()->findClientLeaderGroup(this);
-            if (in_group != NULL && in_group != new_group) {
+            if (in_group != nullptr && in_group != new_group) {
                 in_group->removeMember(this);
-                in_group = NULL;
+                in_group = nullptr;
             }
-            if (new_group == NULL)
+            if (new_group == nullptr)
                 new_group = new Group(None);
             if (in_group != new_group) {
                 in_group = new_group;
@@ -850,7 +850,7 @@
         }
         if (groupTransient()) {
             // no longer transient for ones in the old group
-            if (old_group != NULL) {
+            if (old_group != nullptr) {
                 for (ClientList::ConstIterator it = old_group->members().constBegin();
                         it != old_group->members().constEnd();
                         ++it)
@@ -879,7 +879,7 @@
             addTransient(*it);
         }
     }
-    if (old_group != NULL)
+    if (old_group != nullptr)
         old_group->deref(); // can be now deleted if empty
     checkGroupTransients();
     checkActiveModal();
@@ -890,7 +890,7 @@
 void Client::changeClientLeaderGroup(Group* gr)
 {
     // transientFor() != NULL are in the group of their mainwindow, so keep them there
-    if (transientFor() != NULL)
+    if (transientFor() != nullptr)
         return;
     // also don't change the group for window which have group set
     if (info->groupLeader())
@@ -906,9 +906,9 @@
     // cannot be done in AddTransient(), because there may temporarily
     // exist loops, breaking findModal
     Client* check_modal = dynamic_cast<Client*>(workspace()->mostRecentlyActivatedClient());
-    if (check_modal != NULL && check_modal->check_active_modal) {
+    if (check_modal != nullptr && check_modal->check_active_modal) {
         Client* new_modal = dynamic_cast<Client*>(check_modal->findModal());
-        if (new_modal != NULL && new_modal != check_modal) {
+        if (new_modal != nullptr && new_modal != check_modal) {
             if (!new_modal->isManaged())
                 return; // postpone check until end of manage()
             workspace()->activateClient(new_modal);
diff --git a/input.cpp b/input.cpp
--- a/input.cpp
+++ b/input.cpp
@@ -1647,7 +1647,7 @@
 
 InputRedirection::~InputRedirection()
 {
-    s_self = NULL;
+    s_self = nullptr;
     qDeleteAll(m_filters);
     qDeleteAll(m_spies);
 }
@@ -2129,7 +2129,7 @@
     const bool isScreenLocked = waylandServer() && waylandServer()->isScreenLocked();
     const ToplevelList &stacking = Workspace::self()->stackingOrder();
     if (stacking.isEmpty()) {
-        return NULL;
+        return nullptr;
     }
     auto it = stacking.end();
     do {
@@ -2156,7 +2156,7 @@
             return t;
         }
     } while (it != stacking.begin());
-    return NULL;
+    return nullptr;
 }
 
 Qt::KeyboardModifiers InputRedirection::keyboardModifiers() const
diff --git a/kcmkwin/kwincompositing/compositing.h b/kcmkwin/kwincompositing/compositing.h
--- a/kcmkwin/kwincompositing/compositing.h
+++ b/kcmkwin/kwincompositing/compositing.h
@@ -48,7 +48,7 @@
     Q_PROPERTY(bool windowsBlockCompositing READ windowsBlockCompositing WRITE setWindowsBlockCompositing NOTIFY windowsBlockCompositingChanged)
     Q_PROPERTY(bool compositingRequired READ compositingRequired CONSTANT)
 public:
-    explicit Compositing(QObject *parent = 0);
+    explicit Compositing(QObject *parent = nullptr);
 
     Q_INVOKABLE bool OpenGLIsUnsafe() const;
     Q_INVOKABLE bool OpenGLIsBroken();
@@ -132,7 +132,7 @@
         TypeRole = Qt::UserRole +2
     };
 
-    explicit CompositingType(QObject *parent = 0);
+    explicit CompositingType(QObject *parent = nullptr);
 
     QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override;
     QModelIndex parent(const QModelIndex &child) const override;
diff --git a/kcmkwin/kwincompositing/main.cpp b/kcmkwin/kwincompositing/main.cpp
--- a/kcmkwin/kwincompositing/main.cpp
+++ b/kcmkwin/kwincompositing/main.cpp
@@ -33,7 +33,7 @@
 {
     Q_OBJECT
 public:
-    explicit KWinCompositingSettings(QWidget *parent = 0, const QVariantList &args = QVariantList());
+    explicit KWinCompositingSettings(QWidget *parent = nullptr, const QVariantList &args = QVariantList());
 
 public Q_SLOTS:
     void load() override;
diff --git a/kcmkwin/kwindecoration/declarative-plugin/buttonsmodel.h b/kcmkwin/kwindecoration/declarative-plugin/buttonsmodel.h
--- a/kcmkwin/kwindecoration/declarative-plugin/buttonsmodel.h
+++ b/kcmkwin/kwindecoration/declarative-plugin/buttonsmodel.h
@@ -34,7 +34,7 @@
 {
     Q_OBJECT
 public:
-    explicit ButtonsModel(const QVector< DecorationButtonType > &buttons, QObject *parent = 0);
+    explicit ButtonsModel(const QVector< DecorationButtonType > &buttons, QObject *parent = nullptr);
     explicit ButtonsModel(QObject *parent = nullptr);
     ~ButtonsModel() override;
     QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const override;
diff --git a/kcmkwin/kwindecoration/declarative-plugin/previewitem.cpp b/kcmkwin/kwindecoration/declarative-plugin/previewitem.cpp
--- a/kcmkwin/kwindecoration/declarative-plugin/previewitem.cpp
+++ b/kcmkwin/kwindecoration/declarative-plugin/previewitem.cpp
@@ -78,7 +78,7 @@
     if (m_bridge.isNull() || m_settings.isNull() || m_decoration) {
         return;
     }
-    Decoration *decoration = m_bridge->createDecoration(0);
+    Decoration *decoration = m_bridge->createDecoration(nullptr);
     m_client = m_bridge->lastCreatedClient();
     setDecoration(decoration);
 }
diff --git a/kcmkwin/kwindecoration/declarative-plugin/previewsettings.h b/kcmkwin/kwindecoration/declarative-plugin/previewsettings.h
--- a/kcmkwin/kwindecoration/declarative-plugin/previewsettings.h
+++ b/kcmkwin/kwindecoration/declarative-plugin/previewsettings.h
@@ -37,7 +37,7 @@
 {
     Q_OBJECT
 public:
-    explicit BorderSizesModel(QObject *parent = 0);
+    explicit BorderSizesModel(QObject *parent = nullptr);
     ~BorderSizesModel() override;
     QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const override;
     int rowCount(const QModelIndex& parent = QModelIndex()) const override;
diff --git a/kcmkwin/kwinoptions/mouse.cpp b/kcmkwin/kwinoptions/mouse.cpp
--- a/kcmkwin/kwinoptions/mouse.cpp
+++ b/kcmkwin/kwinoptions/mouse.cpp
@@ -68,7 +68,7 @@
 {
     char const * maxButtonXpms[][3 + 13] = {
         {
-            0, 0, 0,
+            nullptr, nullptr, nullptr,
             "...............",
             ".......#.......",
             "......###......",
@@ -84,7 +84,7 @@
             "..............."
         },
         {
-            0, 0, 0,
+            nullptr, nullptr, nullptr,
             "...............",
             ".......#.......",
             "......###......",
@@ -100,7 +100,7 @@
             "..............."
         },
         {
-            0, 0, 0,
+            nullptr, nullptr, nullptr,
             "...............",
             "...............",
             "...............",
diff --git a/kcmkwin/kwinscreenedges/monitor.h b/kcmkwin/kwinscreenedges/monitor.h
--- a/kcmkwin/kwinscreenedges/monitor.h
+++ b/kcmkwin/kwinscreenedges/monitor.h
@@ -100,7 +100,7 @@
     void mousePressEvent(QGraphicsSceneMouseEvent* e) override;
     void hoverEnterEvent(QGraphicsSceneHoverEvent * e) override;
     void hoverLeaveEvent(QGraphicsSceneHoverEvent * e) override;
-    void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget = 0) override;
+    void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget = nullptr) override;
 private:
     Monitor* monitor;
     Plasma::FrameSvg *button;
diff --git a/kcmkwin/kwintabbox/thumbnailitem.cpp b/kcmkwin/kwintabbox/thumbnailitem.cpp
--- a/kcmkwin/kwintabbox/thumbnailitem.cpp
+++ b/kcmkwin/kwintabbox/thumbnailitem.cpp
@@ -69,7 +69,7 @@
 
 const char* const *BrightnessSaturationShader::attributeNames() const
 {
-    static char const *const names[] = { "vertex", "texCoord", 0 };
+    static char const *const names[] = { "vertex", "texCoord", nullptr };
     return names;
 }
 
diff --git a/layers.cpp b/layers.cpp
--- a/layers.cpp
+++ b/layers.cpp
@@ -267,7 +267,7 @@
                 return c;
         }
     }
-    return 0;
+    return nullptr;
 }
 
 AbstractClient* Workspace::findDesktop(bool topmost, int desktop) const
@@ -288,13 +288,13 @@
                 return client;
         }
     }
-    return NULL;
+    return nullptr;
 }
 
 void Workspace::raiseOrLowerClient(AbstractClient *c)
 {
     if (!c) return;
-    AbstractClient* topmost = NULL;
+    AbstractClient* topmost = nullptr;
 // TODO    Q_ASSERT( block_stacking_updates == 0 );
     if (most_recently_raised && stacking_order.contains(most_recently_raised) &&
             most_recently_raised->isShown(true) && c->isOnCurrentDesktop())
@@ -336,7 +336,7 @@
     }
 
     if (c == most_recently_raised)
-        most_recently_raised = 0;
+        most_recently_raised = nullptr;
 }
 
 void Workspace::lowerClientWithinApplication(AbstractClient* c)
@@ -456,7 +456,7 @@
         for (int i = 0; i < unconstrained_stacking_order.size(); ++i) {
             AbstractClient *other = qobject_cast<AbstractClient*>(unconstrained_stacking_order.at(i));
             if (other && other->layer() == c->layer() && AbstractClient::belongToSameApplication(under, other)) {
-                under = (c == other) ? 0 : other;
+                under = (c == other) ? nullptr : other;
                 break;
             }
         }
@@ -516,7 +516,7 @@
 
         const int screen = (*it)->screen();
         Client *c = qobject_cast<Client*>(*it);
-        QMap< Group*, Layer >::iterator mLayer = minimum_layer[screen].find(c ? c->group() : NULL);
+        QMap< Group*, Layer >::iterator mLayer = minimum_layer[screen].find(c ? c->group() : nullptr);
         if (mLayer != minimum_layer[screen].end()) {
             // If a window is raised above some other window in the same window group
             // which is in the ActiveLayer (i.e. it's fulscreened), make sure it stays
@@ -780,7 +780,7 @@
 
 void Client::restackWindow(xcb_window_t above, int detail, NET::RequestSource src, xcb_timestamp_t timestamp, bool send_event)
 {
-    Client *other = 0;
+    Client *other = nullptr;
     if (detail == XCB_STACK_MODE_OPPOSITE) {
         other = workspace()->findClient(Predicate::WindowMatch, above);
         if (!other) {
@@ -839,7 +839,7 @@
         if (it != begin && (*(it - 1) == other))
             other = qobject_cast<Client*>(*it);
         else
-            other = 0;
+            other = nullptr;
     }
 
     if (other)
diff --git a/libkwineffects/kwinglplatform.cpp b/libkwineffects/kwinglplatform.cpp
--- a/libkwineffects/kwinglplatform.cpp
+++ b/libkwineffects/kwinglplatform.cpp
@@ -38,7 +38,7 @@
 namespace KWin
 {
 
-GLPlatform *GLPlatform::s_platform = 0;
+GLPlatform *GLPlatform::s_platform = nullptr;
 
 static qint64 parseVersionString(const QByteArray &version)
 {
@@ -293,7 +293,7 @@
 {
     QString name = extract(chipset, QStringLiteral("\\bNV[0-9,A-F]{2}\\b")); // NV followed by two hexadecimal digits
     if (!name.isEmpty()) {
-        const int id = chipset.midRef(2, -1).toInt(0, 16); // Strip the 'NV' from the id
+        const int id = chipset.midRef(2, -1).toInt(nullptr, 16); // Strip the 'NV' from the id
 
         switch(id & 0xf0) {
         case 0x00:
diff --git a/libkwineffects/kwinglutils.cpp b/libkwineffects/kwinglutils.cpp
--- a/libkwineffects/kwinglutils.cpp
+++ b/libkwineffects/kwinglutils.cpp
@@ -1968,7 +1968,7 @@
     const size_t minSize = 32768; // Minimum size for streaming buffers
     const size_t alloc = usage != GL_STATIC_DRAW ? align(qMax(size, minSize), 4096) : size;
 
-    glBufferData(GL_ARRAY_BUFFER, alloc, 0, usage);
+    glBufferData(GL_ARRAY_BUFFER, alloc, nullptr, usage);
 
     bufferSize = alloc;
 }
diff --git a/manage.cpp b/manage.cpp
--- a/manage.cpp
+++ b/manage.cpp
@@ -223,7 +223,7 @@
                 desk = NET::OnAllDesktops;
             else if (on_current)
                 desk = VirtualDesktopManager::self()->current();
-            else if (maincl != NULL)
+            else if (maincl != nullptr)
                 desk = maincl->desktop();
 
             if (maincl)
@@ -340,13 +340,13 @@
 
     // Create client group if the window will have a decoration
     bool dontKeepInArea = false;
-    setTabGroup(NULL);
+    setTabGroup(nullptr);
     if (!noBorder() && false) {
         const bool autogrouping = rules()->checkAutogrouping(options->isAutogroupSimilarWindows());
         const bool autogroupInFg = rules()->checkAutogroupInForeground(options->isAutogroupInForeground());
         // Automatically add to previous groups on session restore
         if (session && session->tabGroupClient && !workspace()->hasClient(session->tabGroupClient))
-            session->tabGroupClient = NULL;
+            session->tabGroupClient = nullptr;
         if (session && session->tabGroupClient && session->tabGroupClient != this) {
             tabBehind(session->tabGroupClient, autogroupInFg);
         } else if (isMapped && autogrouping) {
@@ -560,7 +560,7 @@
     updateAllowedActions(true);
 
     // Set initial user time directly
-    m_userTime = readUserTimeMapTimestamp(asn_valid ? &asn_id : NULL, asn_valid ? &asn_data : NULL, session);
+    m_userTime = readUserTimeMapTimestamp(asn_valid ? &asn_id : nullptr, asn_valid ? &asn_data : nullptr, session);
     group()->updateUserTime(m_userTime);   // And do what Client::updateUserTime() does
 
     // This should avoid flicker, because real restacking is done
@@ -582,7 +582,7 @@
         bool allow;
         if (session)
             allow = session->active &&
-                    (!workspace()->wasUserInteraction() || workspace()->activeClient() == NULL ||
+                    (!workspace()->wasUserInteraction() || workspace()->activeClient() == nullptr ||
                      workspace()->activeClient()->isDesktop());
         else
             allow = workspace()->allowClientActivation(this, userTime(), false);
@@ -749,7 +749,7 @@
 {
     // Attempt to find a similar window to the input. If we find multiple possibilities that are in
     // different groups then ignore all of them. This function is for automatic window grouping.
-    Client *found = NULL;
+    Client *found = nullptr;
 
     // See if the window has a group ID to match with
     QString wGId = rules()->checkAutogroupById(QString());
@@ -759,7 +759,7 @@
                 continue; // don't cross activities
             if (wGId == c->rules()->checkAutogroupById(QString())) {
                 if (found && found->tabGroup() != c->tabGroup()) { // We've found two, ignore both
-                    found = NULL;
+                    found = nullptr;
                     break; // Continue to the next test
                 }
                 found = c;
@@ -771,7 +771,7 @@
 
     // If this is a transient window don't take a guess
     if (isTransient())
-        return NULL;
+        return nullptr;
 
     // If we don't have an ID take a guess
     if (rules()->checkAutogrouping(options->isAutogroupSimilarWindows())) {
@@ -784,7 +784,7 @@
                     wRole == wRoleB && // Same window role
                     c->isNormalWindow()) { // Normal window TODO: Can modal windows be "normal"?
                 if (found && found->tabGroup() != c->tabGroup())   // We've found two, ignore both
-                    return NULL;
+                    return nullptr;
                 found = c;
             }
         }
diff --git a/netinfo.cpp b/netinfo.cpp
--- a/netinfo.cpp
+++ b/netinfo.cpp
@@ -33,7 +33,7 @@
 {
 extern int screen_number;
 
-RootInfo *RootInfo::s_self = NULL;
+RootInfo *RootInfo::s_self = nullptr;
 
 RootInfo *RootInfo::create()
 {
@@ -136,7 +136,7 @@
     }
     xcb_window_t supportWindow = s_self->supportWindow();
     delete s_self;
-    s_self = NULL;
+    s_self = nullptr;
     xcb_destroy_window(connection(), supportWindow);
 }
 
@@ -176,7 +176,7 @@
                 workspace->activateClient(c);
             // if activation of the requestor's window would be allowed, allow activation too
             else if (active_window != None
-                    && (c2 = workspace->findClient(Predicate::WindowMatch, active_window)) != NULL
+                    && (c2 = workspace->findClient(Predicate::WindowMatch, active_window)) != nullptr
                     && workspace->allowClientActivation(c2,
                             timestampCompare(timestamp, c2->userTime() > 0 ? timestamp : c2->userTime()), false, true)) {
                 workspace->activateClient(c);
@@ -299,7 +299,7 @@
 
 void WinInfo::disable()
 {
-    m_client = NULL; // only used when the object is passed to Deleted
+    m_client = nullptr; // only used when the object is passed to Deleted
 }
 
 } // namespace
diff --git a/options.h b/options.h
--- a/options.h
+++ b/options.h
@@ -187,7 +187,7 @@
     Q_PROPERTY(bool windowsBlockCompositing READ windowsBlockCompositing WRITE setWindowsBlockCompositing NOTIFY windowsBlockCompositingChanged)
 public:
 
-    explicit Options(QObject *parent = NULL);
+    explicit Options(QObject *parent = nullptr);
     ~Options() override;
 
     void updateSettings();
diff --git a/placement.cpp b/placement.cpp
--- a/placement.cpp
+++ b/placement.cpp
@@ -50,7 +50,7 @@
 
 Placement::~Placement()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 /**
@@ -556,7 +556,7 @@
         ++mains_count;
         place_on2 = *it;
         if ((*it)->isOnCurrentDesktop()) {
-            if (place_on == NULL)
+            if (place_on == nullptr)
                 place_on = *it;
             else {
                 // two or more on current desktop -> center
@@ -570,7 +570,7 @@
             }
         }
     }
-    if (place_on == NULL) {
+    if (place_on == nullptr) {
         // 'mains_count' is used because it doesn't include ignored mainwindows
         if (mains_count != 1) {
             place(c, area, Centered);
diff --git a/platformsupport/scenes/opengl/backend.cpp b/platformsupport/scenes/opengl/backend.cpp
--- a/platformsupport/scenes/opengl/backend.cpp
+++ b/platformsupport/scenes/opengl/backend.cpp
@@ -82,7 +82,7 @@
 
 OverlayWindow* OpenGLBackend::overlayWindow() const
 {
-    return NULL;
+    return nullptr;
 }
 
 QRegion OpenGLBackend::prepareRenderingForScreen(int screenId)
diff --git a/platformsupport/scenes/opengl/linux_dmabuf.cpp b/platformsupport/scenes/opengl/linux_dmabuf.cpp
--- a/platformsupport/scenes/opengl/linux_dmabuf.cpp
+++ b/platformsupport/scenes/opengl/linux_dmabuf.cpp
@@ -461,7 +461,7 @@
 {
     const EGLDisplay eglDisplay = m_backend->eglDisplay();
     EGLint count = 0;
-    EGLBoolean success = eglQueryDmaBufFormatsEXT(eglDisplay, 0, NULL, &count);
+    EGLBoolean success = eglQueryDmaBufFormatsEXT(eglDisplay, 0, nullptr, &count);
 
     if (!success || count == 0) {
         return;
@@ -479,13 +479,13 @@
     for (auto format : qAsConst(formats)) {
         if (eglQueryDmaBufModifiersEXT != nullptr) {
             count = 0;
-            success = eglQueryDmaBufModifiersEXT(eglDisplay, format, 0, NULL, NULL, &count);
+            success = eglQueryDmaBufModifiersEXT(eglDisplay, format, 0, nullptr, nullptr, &count);
 
             if (success && count > 0) {
                 QVector<uint64_t> modifiers(count);
                 if (eglQueryDmaBufModifiersEXT(eglDisplay,
                                                format, count, modifiers.data(),
-                                               NULL, &count)) {
+                                               nullptr, &count)) {
                     QSet<uint64_t> modifiersSet;
                     for (auto mod : qAsConst(modifiers)) {
                         modifiersSet.insert(mod);
diff --git a/plugins/idletime/poller.h b/plugins/idletime/poller.h
--- a/plugins/idletime/poller.h
+++ b/plugins/idletime/poller.h
@@ -41,7 +41,7 @@
     Q_INTERFACES(AbstractSystemPoller)
 
 public:
-    Poller(QObject *parent = 0);
+    Poller(QObject *parent = nullptr);
     ~Poller() override;
 
     bool isAvailable() override;
diff --git a/plugins/kglobalaccel/kglobalaccel_plugin.h b/plugins/kglobalaccel/kglobalaccel_plugin.h
--- a/plugins/kglobalaccel/kglobalaccel_plugin.h
+++ b/plugins/kglobalaccel/kglobalaccel_plugin.h
@@ -31,7 +31,7 @@
     Q_INTERFACES(KGlobalAccelInterface)
 
 public:
-    KGlobalAccelImpl(QObject *parent = 0);
+    KGlobalAccelImpl(QObject *parent = nullptr);
     ~KGlobalAccelImpl() override;
 
     bool grabKey(int key, bool grab) override;
diff --git a/plugins/platforms/wayland/wayland_backend.cpp b/plugins/platforms/wayland/wayland_backend.cpp
--- a/plugins/platforms/wayland/wayland_backend.cpp
+++ b/plugins/platforms/wayland/wayland_backend.cpp
@@ -209,10 +209,10 @@
 }
 
 WaylandSeat::WaylandSeat(wl_seat *seat, WaylandBackend *backend)
-    : QObject(NULL)
+    : QObject(nullptr)
     , m_seat(new Seat(this))
-    , m_pointer(NULL)
-    , m_keyboard(NULL)
+    , m_pointer(nullptr)
+    , m_keyboard(nullptr)
     , m_touch(nullptr)
     , m_enteredSerial(0)
     , m_backend(backend)
diff --git a/plugins/platforms/x11/standalone/glxbackend.cpp b/plugins/platforms/x11/standalone/glxbackend.cpp
--- a/plugins/platforms/x11/standalone/glxbackend.cpp
+++ b/plugins/platforms/x11/standalone/glxbackend.cpp
@@ -108,7 +108,7 @@
     : OpenGLBackend()
     , m_overlayWindow(kwinApp()->platform()->createOverlayWindow())
     , window(None)
-    , fbconfig(NULL)
+    , fbconfig(nullptr)
     , glxWindow(None)
     , ctx(nullptr)
     , m_bufferAge(0)
@@ -271,7 +271,7 @@
         // VirtualBox does not support glxQueryDrawable
         // this should actually be in kwinglutils_funcs, but QueryDrawable seems not to be provided by an extension
         // and the GLPlatform has not been initialized at the moment when initGLX() is called.
-        glXQueryDrawable = NULL;
+        glXQueryDrawable = nullptr;
     }
 
     setIsDirectRendering(bool(glXIsDirect(display(), ctx)));
@@ -337,16 +337,16 @@
         }
         for (auto it = candidates.begin(); it != candidates.end(); it++) {
             const auto attribs = it->build();
-            ctx = glXCreateContextAttribsARB(display(), fbconfig, 0, true, attribs.data());
+            ctx = glXCreateContextAttribsARB(display(), fbconfig, nullptr, true, attribs.data());
             if (ctx) {
                 qCDebug(KWIN_X11STANDALONE) << "Created GLX context with attributes:" << &(*it);
                 break;
             }
         }
     }
 
     if (!ctx)
-        ctx = glXCreateNewContext(display(), fbconfig, GLX_RGBA_TYPE, NULL, direct);
+        ctx = glXCreateNewContext(display(), fbconfig, GLX_RGBA_TYPE, nullptr, direct);
 
     if (!ctx) {
         qCDebug(KWIN_X11STANDALONE) << "Failed to create an OpenGL context.";
@@ -356,7 +356,7 @@
     if (!glXMakeCurrent(display(), glxWindow, ctx)) {
         qCDebug(KWIN_X11STANDALONE) << "Failed to make the OpenGL context current.";
         glXDestroyContext(display(), ctx);
-        ctx = 0;
+        ctx = nullptr;
         return false;
     }
 
@@ -390,7 +390,7 @@
                           0, 0, size.width(), size.height(), 0, XCB_WINDOW_CLASS_INPUT_OUTPUT,
                           visual, XCB_CW_COLORMAP, &colormap);
 
-        glxWindow = glXCreateWindow(display(), fbconfig, window, NULL);
+        glxWindow = glXCreateWindow(display(), fbconfig, window, nullptr);
         overlayWindow()->setup(window);
     } else {
         qCCritical(KWIN_X11STANDALONE) << "Failed to create overlay window";
@@ -885,7 +885,7 @@
 {
     if (options->isGlStrictBinding() && m_glxpixmap) {
         glXReleaseTexImageEXT(display(), m_glxpixmap, GLX_FRONT_LEFT_EXT);
-        glXBindTexImageEXT(display(), m_glxpixmap, GLX_FRONT_LEFT_EXT, NULL);
+        glXBindTexImageEXT(display(), m_glxpixmap, GLX_FRONT_LEFT_EXT, nullptr);
     }
     GLTexturePrivate::onDamage();
 }
diff --git a/plugins/platforms/x11/standalone/overlaywindow_x11.cpp b/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
--- a/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
+++ b/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
@@ -90,7 +90,7 @@
 
 void OverlayWindowX11::setupInputShape(xcb_window_t window)
 {
-    xcb_shape_rectangles(connection(), XCB_SHAPE_SO_SET, XCB_SHAPE_SK_INPUT, XCB_CLIP_ORDERING_UNSORTED, window, 0, 0, 0, NULL);
+    xcb_shape_rectangles(connection(), XCB_SHAPE_SO_SET, XCB_SHAPE_SK_INPUT, XCB_CLIP_ORDERING_UNSORTED, window, 0, 0, 0, nullptr);
 }
 
 void OverlayWindowX11::setNoneBackgroundPixmap(xcb_window_t window)
diff --git a/plugins/platforms/x11/standalone/windowselector.cpp b/plugins/platforms/x11/standalone/windowselector.cpp
--- a/plugins/platforms/x11/standalone/windowselector.cpp
+++ b/plugins/platforms/x11/standalone/windowselector.cpp
@@ -94,7 +94,7 @@
         XCB_EVENT_MASK_POINTER_MOTION |
         XCB_EVENT_MASK_ENTER_WINDOW | XCB_EVENT_MASK_LEAVE_WINDOW,
         XCB_GRAB_MODE_ASYNC, XCB_GRAB_MODE_ASYNC, XCB_WINDOW_NONE,
-        cursor, XCB_TIME_CURRENT_TIME), NULL));
+        cursor, XCB_TIME_CURRENT_TIME), nullptr));
     if (grabPointer.isNull() || grabPointer->status != XCB_GRAB_STATUS_SUCCESS) {
         return false;
     }
@@ -241,7 +241,7 @@
         return;
     }
     xcb_window_t window = window_to_select;
-    Client* client = NULL;
+    Client* client = nullptr;
     while (true) {
         client = Workspace::self()->findClient(Predicate::FrameIdMatch, window);
         if (client) {
diff --git a/plugins/qpa/sharingplatformcontext.cpp b/plugins/qpa/sharingplatformcontext.cpp
--- a/plugins/qpa/sharingplatformcontext.cpp
+++ b/plugins/qpa/sharingplatformcontext.cpp
@@ -109,7 +109,7 @@
 
 void SharingPlatformContext::create()
 {
-    if (config() == 0) {
+    if (config() == nullptr) {
         qCWarning(KWIN_QPA) << "Did not get an EGL config";
         return;
     }
diff --git a/plugins/scenes/opengl/lanczosfilter.h b/plugins/scenes/opengl/lanczosfilter.h
--- a/plugins/scenes/opengl/lanczosfilter.h
+++ b/plugins/scenes/opengl/lanczosfilter.h
@@ -43,7 +43,7 @@
     Q_OBJECT
 
 public:
-    explicit LanczosFilter(QObject* parent = 0);
+    explicit LanczosFilter(QObject* parent = nullptr);
     ~LanczosFilter() override;
     void performPaint(EffectWindowImpl* w, int mask, QRegion region, WindowPaintData& data);
 
diff --git a/plugins/scenes/opengl/lanczosfilter.cpp b/plugins/scenes/opengl/lanczosfilter.cpp
--- a/plugins/scenes/opengl/lanczosfilter.cpp
+++ b/plugins/scenes/opengl/lanczosfilter.cpp
@@ -45,10 +45,10 @@
 
 LanczosFilter::LanczosFilter(QObject* parent)
     : QObject(parent)
-    , m_offscreenTex(0)
-    , m_offscreenTarget(0)
+    , m_offscreenTex(nullptr)
+    , m_offscreenTarget(nullptr)
     , m_inited(false)
-    , m_shader(0)
+    , m_shader(nullptr)
     , m_uOffsets(0)
     , m_uKernel(0)
 {
@@ -240,7 +240,7 @@
                 } else {
                     // offscreen texture not matching - delete
                     delete cachedTexture;
-                    cachedTexture = 0;
+                    cachedTexture = nullptr;
                     w->setData(LanczosCacheRole, QVariant());
                 }
             }
@@ -392,8 +392,8 @@
 
         delete m_offscreenTarget;
         delete m_offscreenTex;
-        m_offscreenTarget = 0;
-        m_offscreenTex = 0;
+        m_offscreenTarget = nullptr;
+        m_offscreenTex = nullptr;
         foreach (Client *c, Workspace::self()->clientList()) {
             discardCacheTexture(c->effectWindow());
         }
diff --git a/plugins/scenes/opengl/scene_opengl.h b/plugins/scenes/opengl/scene_opengl.h
--- a/plugins/scenes/opengl/scene_opengl.h
+++ b/plugins/scenes/opengl/scene_opengl.h
@@ -183,7 +183,7 @@
     struct LeafNode
     {
         LeafNode()
-            : texture(0),
+            : texture(nullptr),
               firstVertex(0),
               vertexCount(0),
               opacity(1.0),
diff --git a/plugins/scenes/opengl/scene_opengl.cpp b/plugins/scenes/opengl/scene_opengl.cpp
--- a/plugins/scenes/opengl/scene_opengl.cpp
+++ b/plugins/scenes/opengl/scene_opengl.cpp
@@ -494,15 +494,15 @@
     }
     if (backend->isFailed()) {
         delete backend;
-        return NULL;
+        return nullptr;
     }
-    SceneOpenGL *scene = NULL;
+    SceneOpenGL *scene = nullptr;
     // first let's try an OpenGL 2 scene
     if (SceneOpenGL2::supported(backend)) {
         scene = new SceneOpenGL2(backend, parent);
         if (scene->initFailed()) {
             delete scene;
-            scene = NULL;
+            scene = nullptr;
         } else {
             return scene;
         }
@@ -918,7 +918,7 @@
 
 SceneOpenGL2::SceneOpenGL2(OpenGLBackend *backend, QObject *parent)
     : SceneOpenGL(backend, parent)
-    , m_lanczosFilter(NULL)
+    , m_lanczosFilter(nullptr)
 {
     if (!init_ok) {
         // base ctor already failed
@@ -1027,7 +1027,7 @@
     GLVertexBuffer *vbo = GLVertexBuffer::streamingBuffer();
     vbo->reset();
     vbo->setUseColor(true);
-    vbo->setData(vertices.count() / 2, 2, vertices.data(), NULL);
+    vbo->setData(vertices.count() / 2, 2, vertices.data(), nullptr);
 
     ShaderBinder binder(ShaderTrait::UniformColor);
     binder.shader()->setUniform(GLShader::ModelViewProjectionMatrix, m_projectionMatrix);
@@ -1060,7 +1060,7 @@
             connect(screens(), &Screens::changed, this, [this]() {
                 makeOpenGLContextCurrent();
                 delete m_lanczosFilter;
-                m_lanczosFilter = NULL;
+                m_lanczosFilter = nullptr;
             });
         }
         m_lanczosFilter->performPaint(w, mask, region, data);
@@ -1074,19 +1074,19 @@
 
 SceneOpenGL::Window::Window(Toplevel* c)
     : Scene::Window(c)
-    , m_scene(NULL)
+    , m_scene(nullptr)
 {
 }
 
 SceneOpenGL::Window::~Window()
 {
 }
 
-static SceneOpenGLTexture *s_frameTexture = NULL;
+static SceneOpenGLTexture *s_frameTexture = nullptr;
 // Bind the window pixmap to an OpenGL texture.
 bool SceneOpenGL::Window::bindTexture()
 {
-    s_frameTexture = NULL;
+    s_frameTexture = nullptr;
     OpenGLWindowPixmap *pixmap = windowPixmap<OpenGLWindowPixmap>();
     if (!pixmap) {
         return false;
@@ -1288,7 +1288,7 @@
 
     if (data.crossFadeProgress() != 1.0) {
         OpenGLWindowPixmap *previous = previousWindowPixmap<OpenGLWindowPixmap>();
-        nodes[PreviousContentLeaf].texture = previous ? previous->texture() : NULL;
+        nodes[PreviousContentLeaf].texture = previous ? previous->texture() : nullptr;
         nodes[PreviousContentLeaf].hasAlpha = !isOpaque();
         nodes[PreviousContentLeaf].opacity = data.opacity() * (1.0 - data.crossFadeProgress());
         nodes[PreviousContentLeaf].coordinateType = NormalizedCoordinates;
@@ -1581,19 +1581,19 @@
 // SceneOpenGL::EffectFrame
 //****************************************
 
-GLTexture* SceneOpenGL::EffectFrame::m_unstyledTexture = NULL;
-QPixmap* SceneOpenGL::EffectFrame::m_unstyledPixmap = NULL;
+GLTexture* SceneOpenGL::EffectFrame::m_unstyledTexture = nullptr;
+QPixmap* SceneOpenGL::EffectFrame::m_unstyledPixmap = nullptr;
 
 SceneOpenGL::EffectFrame::EffectFrame(EffectFrameImpl* frame, SceneOpenGL *scene)
     : Scene::EffectFrame(frame)
-    , m_texture(NULL)
-    , m_textTexture(NULL)
-    , m_oldTextTexture(NULL)
-    , m_textPixmap(NULL)
-    , m_iconTexture(NULL)
-    , m_oldIconTexture(NULL)
-    , m_selectionTexture(NULL)
-    , m_unstyledVBO(NULL)
+    , m_texture(nullptr)
+    , m_textTexture(nullptr)
+    , m_oldTextTexture(nullptr)
+    , m_textPixmap(nullptr)
+    , m_iconTexture(nullptr)
+    , m_oldIconTexture(nullptr)
+    , m_selectionTexture(nullptr)
+    , m_unstyledVBO(nullptr)
     , m_scene(scene)
 {
     if (m_effectFrame->style() == EffectFrameUnstyled && !m_unstyledTexture) {
@@ -1617,55 +1617,55 @@
 {
     glFlush();
     delete m_texture;
-    m_texture = NULL;
+    m_texture = nullptr;
     delete m_textTexture;
-    m_textTexture = NULL;
+    m_textTexture = nullptr;
     delete m_textPixmap;
-    m_textPixmap = NULL;
+    m_textPixmap = nullptr;
     delete m_iconTexture;
-    m_iconTexture = NULL;
+    m_iconTexture = nullptr;
     delete m_selectionTexture;
-    m_selectionTexture = NULL;
+    m_selectionTexture = nullptr;
     delete m_unstyledVBO;
-    m_unstyledVBO = NULL;
+    m_unstyledVBO = nullptr;
     delete m_oldIconTexture;
-    m_oldIconTexture = NULL;
+    m_oldIconTexture = nullptr;
     delete m_oldTextTexture;
-    m_oldTextTexture = NULL;
+    m_oldTextTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::freeIconFrame()
 {
     delete m_iconTexture;
-    m_iconTexture = NULL;
+    m_iconTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::freeTextFrame()
 {
     delete m_textTexture;
-    m_textTexture = NULL;
+    m_textTexture = nullptr;
     delete m_textPixmap;
-    m_textPixmap = NULL;
+    m_textPixmap = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::freeSelection()
 {
     delete m_selectionTexture;
-    m_selectionTexture = NULL;
+    m_selectionTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::crossFadeIcon()
 {
     delete m_oldIconTexture;
     m_oldIconTexture = m_iconTexture;
-    m_iconTexture = NULL;
+    m_iconTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::crossFadeText()
 {
     delete m_oldTextTexture;
     m_oldTextTexture = m_textTexture;
-    m_textTexture = NULL;
+    m_textTexture = nullptr;
 }
 
 void SceneOpenGL::EffectFrame::render(QRegion region, double opacity, double frameOpacity)
@@ -1936,7 +1936,7 @@
 void SceneOpenGL::EffectFrame::updateTexture()
 {
     delete m_texture;
-    m_texture = 0L;
+    m_texture = nullptr;
     if (m_effectFrame->style() == EffectFrameStyled) {
         QPixmap pixmap = m_effectFrame->frame().framePixmap();
         m_texture = new GLTexture(pixmap);
@@ -1946,9 +1946,9 @@
 void SceneOpenGL::EffectFrame::updateTextTexture()
 {
     delete m_textTexture;
-    m_textTexture = 0L;
+    m_textTexture = nullptr;
     delete m_textPixmap;
-    m_textPixmap = 0L;
+    m_textPixmap = nullptr;
 
     if (m_effectFrame->text().isEmpty())
         return;
@@ -1981,9 +1981,9 @@
 void SceneOpenGL::EffectFrame::updateUnstyledTexture()
 {
     delete m_unstyledTexture;
-    m_unstyledTexture = 0L;
+    m_unstyledTexture = nullptr;
     delete m_unstyledPixmap;
-    m_unstyledPixmap = 0L;
+    m_unstyledPixmap = nullptr;
     // Based off circle() from kwinxrenderutils.cpp
 #define CS 8
     m_unstyledPixmap = new QPixmap(2 * CS, 2 * CS);
@@ -2001,9 +2001,9 @@
 void SceneOpenGL::EffectFrame::cleanup()
 {
     delete m_unstyledTexture;
-    m_unstyledTexture = NULL;
+    m_unstyledTexture = nullptr;
     delete m_unstyledPixmap;
-    m_unstyledPixmap = NULL;
+    m_unstyledPixmap = nullptr;
 }
 
 //****************************************
diff --git a/plugins/scenes/qpainter/scene_qpainter.cpp b/plugins/scenes/qpainter/scene_qpainter.cpp
--- a/plugins/scenes/qpainter/scene_qpainter.cpp
+++ b/plugins/scenes/qpainter/scene_qpainter.cpp
@@ -53,7 +53,7 @@
         return nullptr;
     }
     if (backend->isFailed()) {
-        return NULL;
+        return nullptr;
     }
     return new SceneQPainter(backend.take(), parent);
 }
diff --git a/plugins/scenes/xrender/scene_xrender.cpp b/plugins/scenes/xrender/scene_xrender.cpp
--- a/plugins/scenes/xrender/scene_xrender.cpp
+++ b/plugins/scenes/xrender/scene_xrender.cpp
@@ -80,7 +80,7 @@
 
 OverlayWindow* XRenderBackend::overlayWindow()
 {
-    return NULL;
+    return nullptr;
 }
 
 void XRenderBackend::showOverlay()
@@ -146,7 +146,7 @@
     if (haveOverlay) {
         m_overlayWindow->setup(XCB_WINDOW_NONE);
         ScopedCPointer<xcb_get_window_attributes_reply_t> attribs(xcb_get_window_attributes_reply(connection(),
-            xcb_get_window_attributes_unchecked(connection(), m_overlayWindow->window()), NULL));
+            xcb_get_window_attributes_unchecked(connection(), m_overlayWindow->window()), nullptr));
         if (!attribs) {
             setFailed("Failed getting window attributes for overlay window");
             return;
@@ -157,7 +157,7 @@
             return;
         }
         m_front = xcb_generate_id(connection());
-        xcb_render_create_picture(connection(), m_front, m_overlayWindow->window(), m_format, 0, NULL);
+        xcb_render_create_picture(connection(), m_front, m_overlayWindow->window(), m_format, 0, nullptr);
     } else {
         // create XRender picture for the root window
         m_format = XRenderUtils::findPictFormat(defaultScreen()->root_visual);
@@ -178,7 +178,7 @@
     const auto displaySize = screens()->displaySize();
     xcb_create_pixmap(connection(), Xcb::defaultDepth(), pixmap, rootWindow(), displaySize.width(), displaySize.height());
     xcb_render_picture_t b = xcb_generate_id(connection());
-    xcb_render_create_picture(connection(), b, pixmap, m_format, 0, NULL);
+    xcb_render_create_picture(connection(), b, pixmap, m_format, 0, nullptr);
     xcb_free_pixmap(connection(), pixmap);   // The picture owns the pixmap now
     setBuffer(b);
 }
@@ -224,7 +224,7 @@
     QScopedPointer<XRenderBackend> backend;
     backend.reset(new X11XRenderBackend);
     if (backend->isFailed()) {
-        return NULL;
+        return nullptr;
     }
     return new SceneXrender(backend.take(), parent);
 }
@@ -312,7 +312,7 @@
 // SceneXrender::Window
 //****************************************
 
-XRenderPicture *SceneXrender::Window::s_tempPicture = 0;
+XRenderPicture *SceneXrender::Window::s_tempPicture = nullptr;
 QRect SceneXrender::Window::temp_visibleRect;
 XRenderPicture *SceneXrender::Window::s_fadeAlphaPicture = nullptr;
 
@@ -331,7 +331,7 @@
 void SceneXrender::Window::cleanup()
 {
     delete s_tempPicture;
-    s_tempPicture = NULL;
+    s_tempPicture = nullptr;
     delete s_fadeAlphaPicture;
     s_fadeAlphaPicture = nullptr;
 }
@@ -392,7 +392,7 @@
     temp_visibleRect = toplevel->visibleRect().translated(-toplevel->pos());
     if (s_tempPicture && (oldSize.width() < temp_visibleRect.width() || oldSize.height() < temp_visibleRect.height())) {
         delete s_tempPicture;
-        s_tempPicture = NULL;
+        s_tempPicture = nullptr;
         scene_setXRenderOffscreenTarget(0); // invalidate, better crash than cause weird results for developers
     }
     if (!s_tempPicture) {
@@ -768,7 +768,7 @@
         filterName = QByteArray("good");
         break;
     }
-    xcb_render_set_picture_filter(connection(), pic, filterName.length(), filterName.constData(), 0, NULL);
+    xcb_render_set_picture_filter(connection(), pic, filterName.length(), filterName.constData(), 0, nullptr);
 }
 
 WindowPixmap* SceneXrender::Window::createWindowPixmap()
@@ -810,22 +810,22 @@
         return;
     }
     m_picture = xcb_generate_id(connection());
-    xcb_render_create_picture(connection(), m_picture, pixmap(), m_format, 0, NULL);
+    xcb_render_create_picture(connection(), m_picture, pixmap(), m_format, 0, nullptr);
 }
 
 //****************************************
 // SceneXrender::EffectFrame
 //****************************************
 
-XRenderPicture *SceneXrender::EffectFrame::s_effectFrameCircle = NULL;
+XRenderPicture *SceneXrender::EffectFrame::s_effectFrameCircle = nullptr;
 
 SceneXrender::EffectFrame::EffectFrame(EffectFrameImpl* frame)
     : Scene::EffectFrame(frame)
 {
-    m_picture = NULL;
-    m_textPicture = NULL;
-    m_iconPicture = NULL;
-    m_selectionPicture = NULL;
+    m_picture = nullptr;
+    m_textPicture = nullptr;
+    m_iconPicture = nullptr;
+    m_selectionPicture = nullptr;
 }
 
 SceneXrender::EffectFrame::~EffectFrame()
@@ -839,37 +839,37 @@
 void SceneXrender::EffectFrame::cleanup()
 {
     delete s_effectFrameCircle;
-    s_effectFrameCircle = NULL;
+    s_effectFrameCircle = nullptr;
 }
 
 void SceneXrender::EffectFrame::free()
 {
     delete m_picture;
-    m_picture = NULL;
+    m_picture = nullptr;
     delete m_textPicture;
-    m_textPicture = NULL;
+    m_textPicture = nullptr;
     delete m_iconPicture;
-    m_iconPicture = NULL;
+    m_iconPicture = nullptr;
     delete m_selectionPicture;
-    m_selectionPicture = NULL;
+    m_selectionPicture = nullptr;
 }
 
 void SceneXrender::EffectFrame::freeIconFrame()
 {
     delete m_iconPicture;
-    m_iconPicture = NULL;
+    m_iconPicture = nullptr;
 }
 
 void SceneXrender::EffectFrame::freeTextFrame()
 {
     delete m_textPicture;
-    m_textPicture = NULL;
+    m_textPicture = nullptr;
 }
 
 void SceneXrender::EffectFrame::freeSelection()
 {
     delete m_selectionPicture;
-    m_selectionPicture = NULL;
+    m_selectionPicture = nullptr;
 }
 
 void SceneXrender::EffectFrame::crossFadeIcon()
@@ -1038,7 +1038,7 @@
 void SceneXrender::EffectFrame::updatePicture()
 {
     delete m_picture;
-    m_picture = 0L;
+    m_picture = nullptr;
     if (m_effectFrame->style() == EffectFrameStyled) {
         const QPixmap pix = m_effectFrame->frame().framePixmap();
         if (!pix.isNull())
@@ -1050,7 +1050,7 @@
 {
     // Mostly copied from SceneOpenGL::EffectFrame::updateTextTexture() above
     delete m_textPicture;
-    m_textPicture = 0L;
+    m_textPicture = nullptr;
 
     if (m_effectFrame->text().isEmpty()) {
         return;
@@ -1088,7 +1088,7 @@
     :Shadow(toplevel)
 {
     for (int i=0; i<ShadowElementsCount; ++i) {
-        m_pictures[i] = NULL;
+        m_pictures[i] = nullptr;
     }
 }
 
diff --git a/scene.cpp b/scene.cpp
--- a/scene.cpp
+++ b/scene.cpp
@@ -457,7 +457,7 @@
     stacking_order.clear();
 }
 
-static Scene::Window *s_recursionCheck = NULL;
+static Scene::Window *s_recursionCheck = nullptr;
 
 void Scene::paintWindow(Window* w, int mask, QRegion region, WindowQuadList quads)
 {
@@ -593,7 +593,7 @@
         data += QPointF(x, y);
         const int desktopMask = PAINT_SCREEN_TRANSFORMED | PAINT_WINDOW_TRANSFORMED | PAINT_SCREEN_BACKGROUND_FIRST;
         paintDesktop(item->desktop(), desktopMask, clippingRegion, data);
-        s_recursionCheck = NULL;
+        s_recursionCheck = nullptr;
     }
 }
 
@@ -686,13 +686,13 @@
 Scene::Window::Window(Toplevel * c)
     : toplevel(c)
     , filter(ImageFilterFast)
-    , m_shadow(NULL)
+    , m_shadow(nullptr)
     , m_currentPixmap()
     , m_previousPixmap()
     , m_referencePixmapCounter(0)
     , disable_painting(0)
     , shape_valid(false)
-    , cached_quad_list(NULL)
+    , cached_quad_list(nullptr)
 {
 }
 
@@ -839,7 +839,7 @@
 
 WindowQuadList Scene::Window::buildQuads(bool force) const
 {
-    if (cached_quad_list != NULL && !force)
+    if (cached_quad_list != nullptr && !force)
         return *cached_quad_list;
     WindowQuadList ret;
     qreal scale = 1.0;
diff --git a/screenedge.cpp b/screenedge.cpp
--- a/screenedge.cpp
+++ b/screenedge.cpp
@@ -716,7 +716,7 @@
     , m_desktopSwitchingMovingClients(false)
     , m_timeThreshold(0)
     , m_reactivateThreshold(0)
-    , m_virtualDesktopLayout(0)
+    , m_virtualDesktopLayout(nullptr)
     , m_actionTopLeft(ElectricActionNone)
     , m_actionTop(ElectricActionNone)
     , m_actionTopRight(ElectricActionNone)
@@ -735,7 +735,7 @@
 
 ScreenEdges::~ScreenEdges()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 void ScreenEdges::init()
@@ -880,7 +880,7 @@
 void ScreenEdges::updateLayout()
 {
     const QSize desktopMatrix = VirtualDesktopManager::self()->grid().size();
-    Qt::Orientations newLayout = 0;
+    Qt::Orientations newLayout = nullptr;
     if (desktopMatrix.width() > 1) {
         newLayout |= Qt::Horizontal;
     }
diff --git a/screens.cpp b/screens.cpp
--- a/screens.cpp
+++ b/screens.cpp
@@ -74,7 +74,7 @@
 
 Screens::~Screens()
 {
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 void Screens::init()
diff --git a/scripting/dbuscall.h b/scripting/dbuscall.h
--- a/scripting/dbuscall.h
+++ b/scripting/dbuscall.h
@@ -81,7 +81,7 @@
     Q_PROPERTY(QString method READ method WRITE setMethod NOTIFY methodChanged)
     Q_PROPERTY(QVariantList arguments READ arguments WRITE setArguments NOTIFY argumentsChanged)
 public:
-    explicit DBusCall(QObject* parent = 0);
+    explicit DBusCall(QObject* parent = nullptr);
     ~DBusCall() override;
 
     const QString &service() const;
diff --git a/scripting/screenedgeitem.h b/scripting/screenedgeitem.h
--- a/scripting/screenedgeitem.h
+++ b/scripting/screenedgeitem.h
@@ -80,7 +80,7 @@
         Pointer,
         Touch
     };
-    explicit ScreenEdgeItem(QObject *parent = 0);
+    explicit ScreenEdgeItem(QObject *parent = nullptr);
     ~ScreenEdgeItem() override;
     bool isEnabled() const;
     Edge edge() const;
diff --git a/scripting/workspace_wrapper.cpp b/scripting/workspace_wrapper.cpp
--- a/scripting/workspace_wrapper.cpp
+++ b/scripting/workspace_wrapper.cpp
@@ -357,7 +357,7 @@
 
 QQmlListProperty<KWin::AbstractClient> DeclarativeScriptWorkspaceWrapper::clients()
 {
-    return QQmlListProperty<KWin::AbstractClient>(this, 0, &DeclarativeScriptWorkspaceWrapper::countClientList, &DeclarativeScriptWorkspaceWrapper::atClientList);
+    return QQmlListProperty<KWin::AbstractClient>(this, nullptr, &DeclarativeScriptWorkspaceWrapper::countClientList, &DeclarativeScriptWorkspaceWrapper::atClientList);
 }
 
 int DeclarativeScriptWorkspaceWrapper::countClientList(QQmlListProperty<KWin::AbstractClient> *clients)
diff --git a/shadow.cpp b/shadow.cpp
--- a/shadow.cpp
+++ b/shadow.cpp
@@ -51,7 +51,7 @@
 Shadow *Shadow::createShadow(Toplevel *toplevel)
 {
     if (!effects) {
-        return NULL;
+        return nullptr;
     }
     Shadow *shadow = createShadowFromDecoration(toplevel);
     if (!shadow && waylandServer()) {
@@ -78,11 +78,11 @@
 
         if (!shadow->init(data)) {
             delete shadow;
-            return NULL;
+            return nullptr;
         }
         return shadow;
     } else {
-        return NULL;
+        return nullptr;
     }
 }
 
diff --git a/sm.cpp b/sm.cpp
--- a/sm.cpp
+++ b/sm.cpp
@@ -69,7 +69,7 @@
     if (type == -2)   // undefined (not really part of NET::WindowType)
         return "Undefined";
     qFatal("Unknown Window Type");
-    return NULL;
+    return nullptr;
 }
 
 static NET::WindowType txtToWindowType(const char* txt)
@@ -288,7 +288,7 @@
         info->active = (active_client == i);
         info->stackingOrder = cg.readEntry(QLatin1String("stackingOrder") + n, -1);
         info->tabGroup = cg.readEntry(QLatin1String("tabGroup") + n, 0);
-        info->tabGroupClient = NULL;
+        info->tabGroupClient = nullptr;
         info->activities = cg.readEntry(QLatin1String("activities") + n, QStringList());
     }
 }
@@ -319,7 +319,7 @@
  */
 SessionInfo* Workspace::takeSessionInfo(Client* c)
 {
-    SessionInfo *realInfo = 0;
+    SessionInfo *realInfo = nullptr;
     QByteArray sessionId = c->sessionId();
     QByteArray windowRole = c->windowRole();
     QByteArray wmCommand = c->wmCommand();
@@ -444,14 +444,14 @@
     calls.save_complete.client_data = reinterpret_cast< SmPointer >(this);
     calls.shutdown_cancelled.callback = shutdown_cancelled;
     calls.shutdown_cancelled.client_data = reinterpret_cast< SmPointer >(this);
-    char* id = NULL;
+    char* id = nullptr;
     char err[ 11 ];
-    conn = SmcOpenConnection(NULL, 0, 1, 0,
+    conn = SmcOpenConnection(nullptr, nullptr, 1, 0,
                              SmcSaveYourselfProcMask | SmcDieProcMask | SmcSaveCompleteProcMask
-                             | SmcShutdownCancelledProcMask, &calls, NULL, &id, 10, err);
-    if (id != NULL)
+                             | SmcShutdownCancelledProcMask, &calls, nullptr, &id, 10, err);
+    if (id != nullptr)
         free(id);
-    if (conn == NULL)
+    if (conn == nullptr)
         return; // no SM
 
     // detect ksmserver
@@ -470,8 +470,8 @@
     props[ 0 ].num_vals = 1;
     props[ 0 ].vals = &propvalue[ 0 ];
     struct passwd* entry = getpwuid(geteuid());
-    propvalue[ 1 ].length = entry != NULL ? strlen(entry->pw_name) : 0;
-    propvalue[ 1 ].value = (SmPointer)(entry != NULL ? entry->pw_name : "");
+    propvalue[ 1 ].length = entry != nullptr ? strlen(entry->pw_name) : 0;
+    propvalue[ 1 ].value = (SmPointer)(entry != nullptr ? entry->pw_name : "");
     props[ 1 ].name = const_cast< char* >(SmUserID);
     props[ 1 ].type = const_cast< char* >(SmARRAY8);
     props[ 1 ].num_vals = 1;
@@ -508,17 +508,17 @@
 
 void SessionSaveDoneHelper::close()
 {
-    if (conn != NULL) {
+    if (conn != nullptr) {
         delete notifier;
-        SmcCloseConnection(conn, 0, NULL);
+        SmcCloseConnection(conn, 0, nullptr);
     }
-    conn = NULL;
+    conn = nullptr;
 }
 
 void SessionSaveDoneHelper::processData()
 {
-    if (conn != NULL)
-        IceProcessMessages(SmcGetIceConnection(conn), 0, 0);
+    if (conn != nullptr)
+        IceProcessMessages(SmcGetIceConnection(conn), nullptr, nullptr);
 }
 
 void Workspace::sessionSaveDone()
diff --git a/tabbox/tabbox.cpp b/tabbox/tabbox.cpp
--- a/tabbox/tabbox.cpp
+++ b/tabbox/tabbox.cpp
@@ -1475,7 +1475,7 @@
 {
     const auto &list = Workspace::self()->allClientList();
     if (!c || list.isEmpty())
-        return 0;
+        return nullptr;
     int pos = list.indexOf(c);
     if (pos == -1)
         return list.first();
@@ -1493,7 +1493,7 @@
 {
     const auto &list = Workspace::self()->allClientList();
     if (!c || list.isEmpty())
-        return 0;
+        return nullptr;
     int pos = list.indexOf(c);
     if (pos == -1)
         return list.last();
diff --git a/tabgroup.h b/tabgroup.h
--- a/tabgroup.h
+++ b/tabgroup.h
@@ -138,7 +138,7 @@
      * \p main as the primary client to copy the settings off. If \p only is set then only
      * that client is updated to match \p main.
      */
-    void updateStates(AbstractClient* main, States states, AbstractClient* only = NULL);
+    void updateStates(AbstractClient* main, States states, AbstractClient* only = nullptr);
 
     /**
      * updates geometry restrictions of this group, basically called from Client::getWmNormalHints(), otherwise rather private
diff --git a/tabgroup.cpp b/tabgroup.cpp
--- a/tabgroup.cpp
+++ b/tabgroup.cpp
@@ -153,7 +153,7 @@
     if (index < 0)
         return false;
 
-    c->setTabGroup(NULL);
+    c->setTabGroup(nullptr);
 
     m_clients.removeAt(index);
     updateMinMaxSize();
diff --git a/tests/pointerconstraintstest.cpp b/tests/pointerconstraintstest.cpp
--- a/tests/pointerconstraintstest.cpp
+++ b/tests/pointerconstraintstest.cpp
@@ -260,7 +260,7 @@
 void XBackend::init(QQuickView *view)
 {
     Backend::init(view);
-    m_xcbConn = xcb_connect(NULL, NULL);
+    m_xcbConn = xcb_connect(nullptr, nullptr);
     if (!m_xcbConn) {
         qDebug() << "Could not open XCB connection.";
     }
diff --git a/thumbnailitem.h b/thumbnailitem.h
--- a/thumbnailitem.h
+++ b/thumbnailitem.h
@@ -56,7 +56,7 @@
     void clipToChanged();
 
 protected:
-    explicit AbstractThumbnailItem(QQuickItem *parent = 0);
+    explicit AbstractThumbnailItem(QQuickItem *parent = nullptr);
 
 protected Q_SLOTS:
     virtual void repaint(KWin::EffectWindow* w) = 0;
@@ -80,7 +80,7 @@
     Q_PROPERTY(QUuid wId READ wId WRITE setWId NOTIFY wIdChanged SCRIPTABLE true)
     Q_PROPERTY(KWin::AbstractClient *client READ client WRITE setClient NOTIFY clientChanged)
 public:
-    explicit WindowThumbnailItem(QQuickItem *parent = 0);
+    explicit WindowThumbnailItem(QQuickItem *parent = nullptr);
     ~WindowThumbnailItem() override;
 
     QUuid wId() const {
@@ -105,7 +105,7 @@
     Q_OBJECT
     Q_PROPERTY(int desktop READ desktop WRITE setDesktop NOTIFY desktopChanged)
 public:
-    DesktopThumbnailItem(QQuickItem *parent = 0);
+    DesktopThumbnailItem(QQuickItem *parent = nullptr);
     ~DesktopThumbnailItem() override;
 
     int desktop() const {
diff --git a/thumbnailitem.cpp b/thumbnailitem.cpp
--- a/thumbnailitem.cpp
+++ b/thumbnailitem.cpp
@@ -121,8 +121,8 @@
 
 WindowThumbnailItem::WindowThumbnailItem(QQuickItem* parent)
     : AbstractThumbnailItem(parent)
-    , m_wId(0)
-    , m_client(NULL)
+    , m_wId(nullptr)
+    , m_client(nullptr)
 {
 }
 
@@ -136,10 +136,10 @@
         return;
     }
     m_wId = wId;
-    if (m_wId != 0) {
+    if (m_wId != nullptr) {
         setClient(workspace()->findAbstractClient([this] (const AbstractClient *c) { return c->internalId() == m_wId; }));
     } else if (m_client) {
-        m_client = NULL;
+        m_client = nullptr;
         emit clientChanged();
     }
     emit wIdChanged(wId);
diff --git a/toplevel.cpp b/toplevel.cpp
--- a/toplevel.cpp
+++ b/toplevel.cpp
@@ -42,14 +42,14 @@
 Toplevel::Toplevel()
     : m_visual(XCB_NONE)
     , bit_depth(24)
-    , info(NULL)
+    , info(nullptr)
     , ready_for_painting(true)
     , m_isDamaged(false)
     , m_internalId(QUuid::createUuid())
     , m_client()
     , damage_handle(None)
     , is_shape(false)
-    , effect_window(NULL)
+    , effect_window(nullptr)
     , m_clientMachine(new ClientMachine(this))
     , wmClientLeaderWin(0)
     , m_damageReplyPending(false)
@@ -70,7 +70,7 @@
 
 QDebug& operator<<(QDebug& stream, const Toplevel* cl)
 {
-    if (cl == NULL)
+    if (cl == nullptr)
         return stream << "\'NULL\'";
     cl->debug(stream);
     return stream;
@@ -122,7 +122,7 @@
     layer_repaints_region = c->layer_repaints_region;
     is_shape = c->is_shape;
     effect_window = c->effect_window;
-    if (effect_window != NULL)
+    if (effect_window != nullptr)
         effect_window->setWindow(this);
     resource_name = c->resourceName();
     resource_class = c->resourceClass();
@@ -139,7 +139,7 @@
 // owner by Deleted
 void Toplevel::disownDataPassedToDeleted()
 {
-    info = NULL;
+    info = nullptr;
 }
 
 QRect Toplevel::visibleRect() const
@@ -295,13 +295,13 @@
     damage_handle = XCB_NONE;
     damage_region = QRegion();
     repaints_region = QRegion();
-    effect_window = NULL;
+    effect_window = nullptr;
 }
 
 void Toplevel::discardWindowPixmap()
 {
     addDamageFull();
-    if (effectWindow() != NULL && effectWindow()->sceneWindow() != NULL)
+    if (effectWindow() != nullptr && effectWindow()->sceneWindow() != nullptr)
         effectWindow()->sceneWindow()->pixmapDiscarded();
 }
 
@@ -356,7 +356,7 @@
     // Create a new region and copy the damage region to it,
     // resetting the damaged state.
     xcb_xfixes_region_t region = xcb_generate_id(conn);
-    xcb_xfixes_create_region(conn, region, 0, 0);
+    xcb_xfixes_create_region(conn, region, 0, nullptr);
     xcb_damage_subtract(conn, damage_handle, 0, region);
 
     // Send a fetch-region request and destroy the region
@@ -378,7 +378,7 @@
 
     // Get the fetch-region reply
     xcb_xfixes_fetch_region_reply_t *reply =
-            xcb_xfixes_fetch_region_reply(connection(), m_regionCookie, 0);
+            xcb_xfixes_fetch_region_reply(connection(), m_regionCookie, nullptr);
 
     if (!reply)
         return;
@@ -512,7 +512,7 @@
 void Toplevel::deleteEffectWindow()
 {
     delete effect_window;
-    effect_window = NULL;
+    effect_window = nullptr;
 }
 
 void Toplevel::checkScreen()
@@ -595,7 +595,7 @@
 bool Toplevel::hasShadow() const
 {
     if (effectWindow() && effectWindow()->sceneWindow()) {
-        return effectWindow()->sceneWindow()->shadow() != NULL;
+        return effectWindow()->sceneWindow()->shadow() != nullptr;
     }
     return false;
 }
@@ -605,16 +605,16 @@
     if (effectWindow() && effectWindow()->sceneWindow()) {
         return effectWindow()->sceneWindow()->shadow();
     } else {
-        return NULL;
+        return nullptr;
     }
 }
 
 const Shadow *Toplevel::shadow() const
 {
     if (effectWindow() && effectWindow()->sceneWindow()) {
         return effectWindow()->sceneWindow()->shadow();
     } else {
-        return NULL;
+        return nullptr;
     }
 }
 
diff --git a/unmanaged.cpp b/unmanaged.cpp
--- a/unmanaged.cpp
+++ b/unmanaged.cpp
@@ -92,7 +92,7 @@
 
 void Unmanaged::release(ReleaseReason releaseReason)
 {
-    Deleted* del = NULL;
+    Deleted* del = nullptr;
     if (releaseReason != ReleaseReason::KWinShutsDown) {
         del = Deleted::create(this);
     }
diff --git a/useractions.h b/useractions.h
--- a/useractions.h
+++ b/useractions.h
@@ -59,7 +59,7 @@
 {
     Q_OBJECT
 public:
-    explicit UserActionsMenu(QObject *parent = 0);
+    explicit UserActionsMenu(QObject *parent = nullptr);
     ~UserActionsMenu() override;
     /**
      * Discards the constructed menu, so that it gets recreates
diff --git a/useractions.cpp b/useractions.cpp
--- a/useractions.cpp
+++ b/useractions.cpp
@@ -77,25 +77,25 @@
 
 UserActionsMenu::UserActionsMenu(QObject *parent)
     : QObject(parent)
-    , m_menu(NULL)
-    , m_desktopMenu(NULL)
-    , m_screenMenu(NULL)
-    , m_activityMenu(NULL)
-    , m_addTabsMenu(NULL)
-    , m_switchToTabMenu(NULL)
-    , m_scriptsMenu(NULL)
-    , m_resizeOperation(NULL)
-    , m_moveOperation(NULL)
-    , m_maximizeOperation(NULL)
-    , m_shadeOperation(NULL)
-    , m_keepAboveOperation(NULL)
-    , m_keepBelowOperation(NULL)
-    , m_fullScreenOperation(NULL)
-    , m_noBorderOperation(NULL)
-    , m_minimizeOperation(NULL)
-    , m_closeOperation(NULL)
-    , m_removeFromTabGroup(NULL)
-    , m_closeTabGroup(NULL)
+    , m_menu(nullptr)
+    , m_desktopMenu(nullptr)
+    , m_screenMenu(nullptr)
+    , m_activityMenu(nullptr)
+    , m_addTabsMenu(nullptr)
+    , m_switchToTabMenu(nullptr)
+    , m_scriptsMenu(nullptr)
+    , m_resizeOperation(nullptr)
+    , m_moveOperation(nullptr)
+    , m_maximizeOperation(nullptr)
+    , m_shadeOperation(nullptr)
+    , m_keepAboveOperation(nullptr)
+    , m_keepBelowOperation(nullptr)
+    , m_fullScreenOperation(nullptr)
+    , m_noBorderOperation(nullptr)
+    , m_minimizeOperation(nullptr)
+    , m_closeOperation(nullptr)
+    , m_removeFromTabGroup(nullptr)
+    , m_closeTabGroup(nullptr)
 {
 }
 
@@ -171,7 +171,7 @@
     QString type;
     auto shortcut = [](const QString &name) {
         QAction* action = Workspace::self()->findChild<QAction*>(name);
-        Q_ASSERT(action != NULL);
+        Q_ASSERT(action != nullptr);
         const auto shortcuts = KGlobalAccel::self()->shortcut(action);
         return QStringLiteral("%1 (%2)").arg(action->text())
                              .arg(shortcuts.isEmpty() ? QString() : shortcuts.first().toString(QKeySequence::NativeText));
@@ -379,14 +379,14 @@
 void UserActionsMenu::discard()
 {
     delete m_menu;
-    m_menu = NULL;
-    m_desktopMenu = NULL;
+    m_menu = nullptr;
+    m_desktopMenu = nullptr;
     m_multipleDesktopsMenu = nullptr;
-    m_screenMenu = NULL;
-    m_activityMenu = NULL;
-    m_switchToTabMenu = NULL;
-    m_addTabsMenu = NULL;
-    m_scriptsMenu = NULL;
+    m_screenMenu = nullptr;
+    m_activityMenu = nullptr;
+    m_switchToTabMenu = nullptr;
+    m_addTabsMenu = nullptr;
+    m_scriptsMenu = nullptr;
 }
 
 void UserActionsMenu::menuAboutToShow()
@@ -396,15 +396,15 @@
 
     if (VirtualDesktopManager::self()->count() == 1) {
         delete m_desktopMenu;
-        m_desktopMenu = 0;
+        m_desktopMenu = nullptr;
         delete m_multipleDesktopsMenu;
         m_multipleDesktopsMenu = nullptr;
     } else {
         initDesktopPopup();
     }
     if (screens()->count() == 1 || (!m_client->isMovable() && !m_client->isMovableAcrossScreens())) {
         delete m_screenMenu;
-        m_screenMenu = NULL;
+        m_screenMenu = nullptr;
     } else {
         initScreenPopup();
     }
@@ -431,12 +431,12 @@
         m_addTabsMenu->setPalette(m_client->palette());
     } else {
         delete m_addTabsMenu;
-        m_addTabsMenu = 0;
+        m_addTabsMenu = nullptr;
     }
 
     // drop the existing scripts menu
     delete m_scriptsMenu;
-    m_scriptsMenu = NULL;
+    m_scriptsMenu = nullptr;
     // ask scripts whether they want to add entries for the given Client
     QList<QAction*> scriptActions = Scripting::self()->actionsForUserActionMenu(m_client.data(), m_scriptsMenu);
     if (!scriptActions.isEmpty()) {
@@ -466,7 +466,7 @@
     qCDebug(KWIN_CORE) << "activities:" << openActivities_.size();
     if (openActivities_.size() < 2) {
         delete m_activityMenu;
-        m_activityMenu = 0;
+        m_activityMenu = nullptr;
     } else {
         initActivityPopup();
     }
@@ -570,7 +570,7 @@
         }
     } else {
         delete m_switchToTabMenu;
-        m_switchToTabMenu = 0;
+        m_switchToTabMenu = nullptr;
     }
 
     if (!m_addTabsMenu) {
@@ -1075,8 +1075,8 @@
 {
     if (active_popup) {
         active_popup->close();
-        active_popup = NULL;
-        active_popup_client = NULL;
+        active_popup = nullptr;
+        active_popup_client = nullptr;
     }
     m_userActionsMenu->close();
 }
@@ -1120,7 +1120,7 @@
 
 void Workspace::setupWindowShortcut(AbstractClient* c)
 {
-    Q_ASSERT(client_keys_dialog == NULL);
+    Q_ASSERT(client_keys_dialog == nullptr);
     // TODO: PORT ME (KGlobalAccel related)
     //keys->setEnabled( false );
     //disable_shortcuts_keys->setEnabled( false );
@@ -1150,8 +1150,8 @@
         client_keys_client->setShortcut(client_keys_dialog->shortcut().toString());
     closeActivePopup();
     client_keys_dialog->deleteLater();
-    client_keys_dialog = NULL;
-    client_keys_client = NULL;
+    client_keys_dialog = nullptr;
+    client_keys_client = nullptr;
     if (active_client)
         active_client->takeFocus();
 }
@@ -1161,7 +1161,7 @@
     QString key = QStringLiteral("_k_session:%1").arg(c->window());
     QAction* action = findChild<QAction*>(key);
     if (!c->shortcut().isEmpty()) {
-        if (action == NULL) { // new shortcut
+        if (action == nullptr) { // new shortcut
             action = new QAction(this);
             kwinApp()->platform()->setupActionForGlobalAccel(action);
             action->setProperty("componentName", QStringLiteral(KWIN_NAME));
diff --git a/utils.cpp b/utils.cpp
--- a/utils.cpp
+++ b/utils.cpp
@@ -107,17 +107,17 @@
 
 bool grabXKeyboard(xcb_window_t w)
 {
-    if (QWidget::keyboardGrabber() != NULL)
+    if (QWidget::keyboardGrabber() != nullptr)
         return false;
     if (keyboard_grabbed)
         return false;
-    if (qApp->activePopupWidget() != NULL)
+    if (qApp->activePopupWidget() != nullptr)
         return false;
     if (w == XCB_WINDOW_NONE)
         w = rootWindow();
     const xcb_grab_keyboard_cookie_t c = xcb_grab_keyboard_unchecked(connection(), false, w, xTime(),
                                                                      XCB_GRAB_MODE_ASYNC, XCB_GRAB_MODE_ASYNC);
-    ScopedCPointer<xcb_grab_keyboard_reply_t> grab(xcb_grab_keyboard_reply(connection(), c, NULL));
+    ScopedCPointer<xcb_grab_keyboard_reply_t> grab(xcb_grab_keyboard_reply(connection(), c, nullptr));
     if (grab.isNull()) {
         return false;
     }
diff --git a/virtualdesktops.cpp b/virtualdesktops.cpp
--- a/virtualdesktops.cpp
+++ b/virtualdesktops.cpp
@@ -232,13 +232,13 @@
 VirtualDesktopManager::VirtualDesktopManager(QObject *parent)
     : QObject(parent)
     , m_navigationWrapsAround(false)
-    , m_rootInfo(NULL)
+    , m_rootInfo(nullptr)
 {
 }
 
 VirtualDesktopManager::~VirtualDesktopManager()
 {
-    s_manager = NULL;
+    s_manager = nullptr;
 }
 
 void VirtualDesktopManager::setRootInfo(NETRootInfo *info)
diff --git a/workspace.h b/workspace.h
--- a/workspace.h
+++ b/workspace.h
@@ -331,7 +331,7 @@
     void focusToNull(); // SELI TODO: Public?
 
     void clientShortcutUpdated(AbstractClient* c);
-    bool shortcutAvailable(const QKeySequence &cut, AbstractClient* ignore = NULL) const;
+    bool shortcutAvailable(const QKeySequence &cut, AbstractClient* ignore = nullptr) const;
     bool globalShortcutsDisabled() const;
     void disableGlobalShortcutsForClient(bool disable);
 
diff --git a/workspace.cpp b/workspace.cpp
--- a/workspace.cpp
+++ b/workspace.cpp
@@ -99,31 +99,31 @@
     }
 }
 
-Workspace* Workspace::_self = 0;
+Workspace* Workspace::_self = nullptr;
 
 Workspace::Workspace(const QString &sessionKey)
-    : QObject(0)
-    , m_compositor(NULL)
+    : QObject(nullptr)
+    , m_compositor(nullptr)
     // Unsorted
-    , active_popup(NULL)
-    , active_popup_client(NULL)
+    , active_popup(nullptr)
+    , active_popup_client(nullptr)
     , m_initialDesktop(1)
-    , active_client(0)
-    , last_active_client(0)
-    , most_recently_raised(0)
-    , movingClient(0)
-    , delayfocus_client(0)
+    , active_client(nullptr)
+    , last_active_client(nullptr)
+    , most_recently_raised(nullptr)
+    , movingClient(nullptr)
+    , delayfocus_client(nullptr)
     , force_restacking(false)
     , showing_desktop(false)
     , was_user_interaction(false)
     , session_saving(false)
     , block_focus(0)
     , m_userActionsMenu(new UserActionsMenu(this))
-    , client_keys_dialog(NULL)
-    , client_keys_client(NULL)
+    , client_keys_dialog(nullptr)
+    , client_keys_client(nullptr)
     , global_shortcuts_disabled_for_client(false)
     , workspaceInit(true)
-    , startup(0)
+    , startup(nullptr)
     , set_active_client_recursion(0)
     , block_stacking_updates(0)
 {
@@ -150,7 +150,7 @@
     options->loadConfig();
     options->loadCompositingConfig(false);
 
-    delayFocusTimer = 0;
+    delayFocusTimer = nullptr;
 
     if (!sessionKey.isEmpty())
         loadSessionInfo(sessionKey);
@@ -281,7 +281,7 @@
                                           QStringLiteral("refreshFonts"),
                                           this, SLOT(reconfigure()));
 
-    active_client = NULL;
+    active_client = nullptr;
 
     initWithX11();
 
@@ -517,15 +517,15 @@
         --block_focus;
         new_active_client = findClient(Predicate::WindowMatch, client_info.activeWindow());
     }
-    if (new_active_client == NULL
-            && activeClient() == NULL && should_get_focus.count() == 0) {
+    if (new_active_client == nullptr
+            && activeClient() == nullptr && should_get_focus.count() == 0) {
         // No client activated in manage()
-        if (new_active_client == NULL)
+        if (new_active_client == nullptr)
             new_active_client = topClientOnDesktop(VirtualDesktopManager::self()->current(), -1);
-        if (new_active_client == NULL && !desktops.isEmpty())
+        if (new_active_client == nullptr && !desktops.isEmpty())
             new_active_client = findDesktop(true, VirtualDesktopManager::self()->current());
     }
-    if (new_active_client != NULL)
+    if (new_active_client != nullptr)
         activateClient(new_active_client);
 }
 
@@ -581,7 +581,7 @@
     // TODO: ungrabXServer();
 
     Xcb::Extensions::destroy();
-    _self = 0;
+    _self = nullptr;
 }
 
 void Workspace::setupClientConnections(AbstractClient *c)
@@ -602,20 +602,20 @@
     connect(c, SIGNAL(clientFullScreenSet(KWin::Client*,bool,bool)), ScreenEdges::self(), SIGNAL(checkBlocking()));
     if (!c->manage(w, is_mapped)) {
         Client::deleteClient(c);
-        return NULL;
+        return nullptr;
     }
     addClient(c);
     return c;
 }
 
 Unmanaged* Workspace::createUnmanaged(xcb_window_t w)
 {
     if (m_compositor && m_compositor->checkForOverlayWindow(w))
-        return NULL;
+        return nullptr;
     Unmanaged* c = new Unmanaged();
     if (!c->track(w)) {
         Unmanaged::deleteUnmanaged(c);
-        return NULL;
+        return nullptr;
     }
     connect(c, &Unmanaged::needsRepaint, m_compositor, &Compositor::scheduleRepaint);
     addUnmanaged(c);
@@ -629,12 +629,12 @@
 
     emit clientAdded(c);
 
-    if (grp != NULL)
+    if (grp != nullptr)
         grp->gotLeader(c);
 
     if (c->isDesktop()) {
         desktops.append(c);
-        if (active_client == NULL && should_get_focus.isEmpty() && c->isOnCurrentDesktop())
+        if (active_client == nullptr && should_get_focus.isEmpty() && c->isOnCurrentDesktop())
             requestFocus(c);   // TODO: Make sure desktop is active after startup if there's no other window active
     } else {
         FocusChain::self()->update(c, FocusChain::Update);
@@ -651,7 +651,7 @@
     if (c->isDesktop()) {
         raiseClient(c);
         // If there's no active client, make this desktop the active one
-        if (activeClient() == NULL && should_get_focus.count() == 0)
+        if (activeClient() == nullptr && should_get_focus.count() == 0)
             activateClient(findDesktop(true, VirtualDesktopManager::self()->current()));
     }
     c->checkActiveModal();
@@ -696,15 +696,15 @@
     markXStackingOrderAsDirty();
     attention_chain.removeAll(c);
     Group* group = findGroup(c->window());
-    if (group != NULL)
+    if (group != nullptr)
         group->lostLeader();
 
     if (c == most_recently_raised)
-        most_recently_raised = 0;
+        most_recently_raised = nullptr;
     should_get_focus.removeAll(c);
     Q_ASSERT(c != active_client);
     if (c == last_active_client)
-        last_active_client = 0;
+        last_active_client = nullptr;
     if (c == delayfocus_client)
         cancelDelayFocus();
 
@@ -798,14 +798,14 @@
             if (!c->isTransient()) {
                 if (!c->group() || c->group()->members().count() == 1)   // Has its own group, keep always visible
                     show = true;
-                else if (client != NULL && c->group() == client->group())
+                else if (client != nullptr && c->group() == client->group())
                     show = true;
                 else
                     show = false;
             } else {
-                if (group != NULL && c->group() == group)
+                if (group != nullptr && c->group() == group)
                     show = true;
-                else if (client != NULL && client->hasTransient(c, true))
+                else if (client != nullptr && client->hasTransient(c, true))
                     show = true;
                 else
                     show = false;
@@ -955,7 +955,7 @@
 
 void Workspace::activateClientOnNewDesktop(uint desktop)
 {
-    AbstractClient* c = NULL;
+    AbstractClient* c = nullptr;
     if (options->focusPolicyIsReasonable()) {
         c = findClientToActivateOnDesktop(desktop);
     }
@@ -965,11 +965,11 @@
     else if (active_client && active_client->isShown(true) && active_client->isOnCurrentDesktop())
         c = active_client;
 
-    if (c == NULL && !desktops.isEmpty())
+    if (c == nullptr && !desktops.isEmpty())
         c = findDesktop(true, desktop);
 
     if (c != active_client)
-        setActiveClient(NULL);
+        setActiveClient(nullptr);
 
     if (c)
         requestFocus(c);
@@ -981,7 +981,7 @@
 
 AbstractClient *Workspace::findClientToActivateOnDesktop(uint desktop)
 {
-    if (movingClient != NULL && active_client == movingClient &&
+    if (movingClient != nullptr && active_client == movingClient &&
         FocusChain::self()->contains(active_client, desktop) &&
         active_client->isShown(true) && active_client->isOnCurrentDesktop()) {
         // A requestFocus call will fail, as the client is already active
@@ -1068,7 +1068,7 @@
 
     // Restore the focus on this desktop
     --block_focus;
-    AbstractClient* c = 0;
+    AbstractClient* c = nullptr;
 
     //FIXME below here is a lot of focuschain stuff, probably all wrong now
     if (options->focusPolicyIsReasonable()) {
@@ -1081,11 +1081,11 @@
     else if (active_client && active_client->isShown(true) && active_client->isOnCurrentDesktop() && active_client->isOnCurrentActivity())
         c = active_client;
 
-    if (c == NULL && !desktops.isEmpty())
+    if (c == nullptr && !desktops.isEmpty())
         c = findDesktop(true, VirtualDesktopManager::self()->current());
 
     if (c != active_client)
-        setActiveClient(NULL);
+        setActiveClient(nullptr);
 
     if (c)
         requestFocus(c);
@@ -1243,7 +1243,7 @@
 void Workspace::cancelDelayFocus()
 {
     delete delayFocusTimer;
-    delayFocusTimer = 0;
+    delayFocusTimer = nullptr;
 }
 
 bool Workspace::checkStartupNotification(xcb_window_t w, KStartupInfoId &id, KStartupInfoData &data)
diff --git a/xcbutils.h b/xcbutils.h
--- a/xcbutils.h
+++ b/xcbutils.h
@@ -263,11 +263,11 @@
     }
     inline bool isNull() {
         getReply();
-        return m_reply == NULL;
+        return m_reply == nullptr;
     }
     inline bool isNull() const {
         const_cast<AbstractWrapper*>(this)->getReply();
-        return m_reply == NULL;
+        return m_reply == nullptr;
     }
     inline operator bool() {
         return !isNull();
@@ -299,31 +299,31 @@
     inline Reply *take() {
         getReply();
         Reply *ret = m_reply;
-        m_reply = NULL;
+        m_reply = nullptr;
         m_window = XCB_WINDOW_NONE;
         return ret;
     }
 
 protected:
     AbstractWrapper()
         : m_retrieved(false)
         , m_window(XCB_WINDOW_NONE)
-        , m_reply(NULL)
+        , m_reply(nullptr)
     {
         m_cookie.sequence = 0;
     }
     explicit AbstractWrapper(WindowId window, Cookie cookie)
         : m_retrieved(false)
         , m_cookie(cookie)
         , m_window(window)
-        , m_reply(NULL)
+        , m_reply(nullptr)
     {
     }
     explicit AbstractWrapper(const AbstractWrapper &other)
         : m_retrieved(other.m_retrieved)
         , m_cookie(other.m_cookie)
         , m_window(other.m_window)
-        , m_reply(NULL)
+        , m_reply(nullptr)
     {
         takeFromOther(const_cast<AbstractWrapper&>(other));
     }
@@ -1332,7 +1332,7 @@
      * @param values The values to be passed to xcb_create_window
      * @param parent The parent window
      */
-    Window(const QRect &geometry, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    Window(const QRect &geometry, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     /**
      * Creates an xcb_window_t and manages it. It's a convenient method to create a window with
      * depth and visual being copied from parent and border being @c 0.
@@ -1342,7 +1342,7 @@
      * @param values The values to be passed to xcb_create_window
      * @param parent The parent window
      */
-    Window(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    Window(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     Window(const Window &other) = delete;
     ~Window();
 
@@ -1356,7 +1356,7 @@
      * @param values The values to be passed to xcb_create_window
      * @param parent The parent window
      */
-    void create(const QRect &geometry, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    void create(const QRect &geometry, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     /**
      * Creates a new window for which the responsibility is taken over. If a window had been managed
      * before it is freed.
@@ -1368,7 +1368,7 @@
      * @param values The values to be passed to xcb_create_window
      * @param parent The parent window
      */
-    void create(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    void create(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     /**
      * Frees the existing window and starts to manage the new @p window.
      * If @p destroy is @c true the new managed window will be destroyed together with this
@@ -1419,7 +1419,7 @@
     void kill();
     operator xcb_window_t() const;
 private:
-    xcb_window_t doCreate(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = NULL, xcb_window_t parent = rootWindow());
+    xcb_window_t doCreate(const QRect &geometry, uint16_t windowClass, uint32_t mask = 0, const uint32_t *values = nullptr, xcb_window_t parent = rootWindow());
     void destroy();
     xcb_window_t m_window;
     bool m_destroy;
diff --git a/xcbutils.cpp b/xcbutils.cpp
--- a/xcbutils.cpp
+++ b/xcbutils.cpp
@@ -343,11 +343,11 @@
 template<typename reply, typename T, typename F>
 void Extensions::initVersion(T cookie, F f, ExtensionData *dataToFill)
 {
-    ScopedCPointer<reply> version(f(connection(), cookie, NULL));
+    ScopedCPointer<reply> version(f(connection(), cookie, nullptr));
     dataToFill->version = version->major_version * 0x10 + version->minor_version;
 }
 
-Extensions *Extensions::s_self = NULL;
+Extensions *Extensions::s_self = nullptr;
 
 Extensions *Extensions::self()
 {
@@ -360,7 +360,7 @@
 void Extensions::destroy()
 {
     delete s_self;
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 Extensions::Extensions()
@@ -499,7 +499,7 @@
         return false;
     }
     ScopedCPointer<xcb_shape_query_extents_reply_t> extents(xcb_shape_query_extents_reply(
-        connection(), xcb_shape_query_extents_unchecked(connection(), w), NULL));
+        connection(), xcb_shape_query_extents_unchecked(connection(), w), nullptr));
     if (extents.isNull()) {
         return false;
     }
@@ -560,7 +560,7 @@
 //****************************************
 Shm::Shm()
     : m_shmId(-1)
-    , m_buffer(NULL)
+    , m_buffer(nullptr)
     , m_segment(XCB_NONE)
     , m_valid(false)
     , m_pixmapFormat(XCB_IMAGE_FORMAT_XY_BITMAP)
@@ -584,7 +584,7 @@
         return false;
     }
     ScopedCPointer<xcb_shm_query_version_reply_t> version(xcb_shm_query_version_reply(connection(),
-        xcb_shm_query_version_unchecked(connection()), NULL));
+        xcb_shm_query_version_unchecked(connection()), nullptr));
     if (version.isNull()) {
         qCDebug(KWIN_CORE) << "Failed to get SHM extension version information";
         return false;
@@ -596,13 +596,13 @@
         qCDebug(KWIN_CORE) << "Failed to allocate SHM segment";
         return false;
     }
-    m_buffer = shmat(m_shmId, NULL, 0 /*read/write*/);
+    m_buffer = shmat(m_shmId, nullptr, 0 /*read/write*/);
     if (-1 == reinterpret_cast<long>(m_buffer)) {
         qCDebug(KWIN_CORE) << "Failed to attach SHM segment";
-        shmctl(m_shmId, IPC_RMID, NULL);
+        shmctl(m_shmId, IPC_RMID, nullptr);
         return false;
     }
-    shmctl(m_shmId, IPC_RMID, NULL);
+    shmctl(m_shmId, IPC_RMID, nullptr);
 
     m_segment = xcb_generate_id(connection());
     const xcb_void_cookie_t cookie = xcb_shm_attach_checked(connection(), m_segment, m_shmId, false);
diff --git a/xkb.cpp b/xkb.cpp
--- a/xkb.cpp
+++ b/xkb.cpp
@@ -69,8 +69,8 @@
 Xkb::Xkb(QObject *parent)
     : QObject(parent)
     , m_context(xkb_context_new(XKB_CONTEXT_NO_FLAGS))
-    , m_keymap(NULL)
-    , m_state(NULL)
+    , m_keymap(nullptr)
+    , m_state(nullptr)
     , m_shiftModifier(0)
     , m_capsModifier(0)
     , m_controlModifier(0)
@@ -206,7 +206,7 @@
     if (!m_context) {
         return;
     }
-    char *map = reinterpret_cast<char*>(mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0));
+    char *map = reinterpret_cast<char*>(mmap(nullptr, size, PROT_READ, MAP_SHARED, fd, 0));
     if (map == MAP_FAILED) {
         return;
     }
diff --git a/xwl/drag_x.cpp b/xwl/drag_x.cpp
--- a/xwl/drag_x.cpp
+++ b/xwl/drag_x.cpp
@@ -408,8 +408,8 @@
                                    XCB_GET_PROPERTY_TYPE_ANY,
                                    0, 0x1fffffff);
 
-    auto *reply = xcb_get_property_reply(xcbConn, cookie, NULL);
-    if (reply == NULL) {
+    auto *reply = xcb_get_property_reply(xcbConn, cookie, nullptr);
+    if (reply == nullptr) {
         return;
     }
     if (reply->type != XCB_ATOM_ATOM || reply->value_len == 0) {
diff --git a/xwl/transfer.cpp b/xwl/transfer.cpp
--- a/xwl/transfer.cpp
+++ b/xwl/transfer.cpp
@@ -265,7 +265,7 @@
                                 m_request->requestor,
                                 m_request->property,
                                 m_request->target,
-                                8, 0, NULL);
+                                8, 0, nullptr);
             xcb_flush(xcbConn);
             m_flushPropertyOnDelete = false;
             endTransfer();
@@ -375,8 +375,8 @@
                                    0x1fffffff
                                    );
 
-    auto *reply = xcb_get_property_reply(xcbConn, cookie, NULL);
-    if (reply == NULL) {
+    auto *reply = xcb_get_property_reply(xcbConn, cookie, nullptr);
+    if (reply == nullptr) {
         qCWarning(KWIN_XWL) << "Can't get selection property.";
         endTransfer();
         return;