diff --git a/common/carddav-contacts-sync/auth.cpp b/common/carddav-contacts-sync/auth.cpp
--- a/common/carddav-contacts-sync/auth.cpp
+++ b/common/carddav-contacts-sync/auth.cpp
@@ -46,9 +46,9 @@
 
 Auth::Auth(QObject *parent)
     : QObject(parent)
-    , m_account(0)
-    , m_ident(0)
-    , m_session(0)
+    , m_account(nullptr)
+    , m_ident(nullptr)
+    , m_session(nullptr)
     , m_ignoreSslErrors(false)
 {
 }
@@ -98,7 +98,7 @@
         return;
     }
 
-    m_ident = m_account->credentialsId() > 0 ? SignOn::Identity::existingIdentity(m_account->credentialsId()) : 0;
+    m_ident = m_account->credentialsId() > 0 ? SignOn::Identity::existingIdentity(m_account->credentialsId()) : nullptr;
     if (!m_ident) {
         qWarning() << "no valid credentials for account" << accountId;
         Q_EMIT signInError();
diff --git a/common/carddav-contacts-sync/carddav-plugin.h b/common/carddav-contacts-sync/carddav-plugin.h
--- a/common/carddav-contacts-sync/carddav-plugin.h
+++ b/common/carddav-contacts-sync/carddav-plugin.h
@@ -34,7 +34,7 @@
     Q_INTERFACES(KAccountsDPlugin)
 
 public:
-    KAccountsCardDavPlugin(QObject *parent = 0);
+    KAccountsCardDavPlugin(QObject *parent = nullptr);
     ~KAccountsCardDavPlugin();
 
 public Q_SLOTS:
diff --git a/common/carddav-contacts-sync/carddav-plugin.cpp b/common/carddav-contacts-sync/carddav-plugin.cpp
--- a/common/carddav-contacts-sync/carddav-plugin.cpp
+++ b/common/carddav-contacts-sync/carddav-plugin.cpp
@@ -140,7 +140,7 @@
 
     qDebug() << "Using: host:" << carddavUrl.host() << "path:" << carddavUrl.path();
 
-    Syncer *s = new Syncer(0);
+    Syncer *s = new Syncer(nullptr);
     s->setProperty("accountId", credentialsJob->accountId());
 
     const QString &userName = data.value("AccountUsername").toString();
diff --git a/common/carddav-contacts-sync/requestgenerator.cpp b/common/carddav-contacts-sync/requestgenerator.cpp
--- a/common/carddav-contacts-sync/requestgenerator.cpp
+++ b/common/carddav-contacts-sync/requestgenerator.cpp
@@ -153,7 +153,7 @@
 {
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     QString requestStr = QStringLiteral(
@@ -170,12 +170,12 @@
 {
     if (Q_UNLIKELY(userPath.isEmpty())) {
         qWarning() << "user path empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     QString requestStr = QStringLiteral(
@@ -192,12 +192,12 @@
 {
     if (Q_UNLIKELY(userAddressbooksPath.isEmpty())) {
         qWarning() << "addressbooks path empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     QString requestStr = QStringLiteral(
@@ -216,12 +216,12 @@
 {
     if (Q_UNLIKELY(addressbookPath.isEmpty())) {
         qWarning() << "addressbook path empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     QString requestStr = QStringLiteral(
@@ -239,17 +239,17 @@
 {
     if (Q_UNLIKELY(syncToken.isEmpty())) {
         qWarning() << "sync token empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(addressbookUrl.isEmpty())) {
         qWarning() << "addressbook url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     QString requestStr = QStringLiteral(
@@ -269,12 +269,12 @@
 {
     if (Q_UNLIKELY(addressbookPath.isEmpty())) {
         qWarning() << "addressbook path empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     QString requestStr = QStringLiteral(
@@ -291,17 +291,17 @@
 {
     if (Q_UNLIKELY(contactEtags.isEmpty())) {
         qWarning() << "etag list empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(addressbookPath.isEmpty())) {
         qWarning() << "addressbook path empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     // Note: this may not work with all cardDav servers, since according to the RFC:
@@ -323,17 +323,17 @@
 {
     if (Q_UNLIKELY(contactUris.isEmpty())) {
         qWarning() << "etag list empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(addressbookPath.isEmpty())) {
         qWarning() << "addressbook path empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     QString uriHrefs;
@@ -369,19 +369,19 @@
 {
     if (Q_UNLIKELY(vcard.isEmpty())) {
         qWarning() << "vcard empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     // the etag can be empty if it's an addition
 
     if (Q_UNLIKELY(contactPath.isEmpty())) {
         qWarning() << "contact uri empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     return generateUpsyncRequest(serverUrl, contactPath, etag,
@@ -393,17 +393,17 @@
 {
     if (Q_UNLIKELY(etag.isEmpty())) {
         qWarning() << "etag empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(contactPath.isEmpty())) {
         qWarning() << "contact uri empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     if (Q_UNLIKELY(serverUrl.isEmpty())) {
         qWarning() << "server url empty, aborting";
-        return 0;
+        return nullptr;
     }
 
     return generateUpsyncRequest(serverUrl, contactPath, etag, QString(),
diff --git a/common/carddav-contacts-sync/syncer.cpp b/common/carddav-contacts-sync/syncer.cpp
--- a/common/carddav-contacts-sync/syncer.cpp
+++ b/common/carddav-contacts-sync/syncer.cpp
@@ -66,8 +66,8 @@
 Syncer::Syncer(QObject *parent/*, Buteo::SyncProfile *syncProfile*/)
     : QObject(parent) //, QtContactsSqliteExtensions::TwoWayContactSyncAdapter(CARDDAV_CONTACTS_SYNCTARGET)
 //     , m_syncProfile(syncProfile)
-    , m_cardDav(0)
-    , m_auth(0)
+    , m_cardDav(nullptr)
+    , m_auth(nullptr)
     , m_syncAborted(false)
     , m_syncError(false)
     , m_accountId(0)
diff --git a/google/google-contacts-sync/google-contacts-plugin.h b/google/google-contacts-sync/google-contacts-plugin.h
--- a/google/google-contacts-sync/google-contacts-plugin.h
+++ b/google/google-contacts-sync/google-contacts-plugin.h
@@ -38,7 +38,7 @@
     Q_INTERFACES(KAccountsDPlugin)
 
 public:
-    GoogleContactsPlugin(QObject *parent = 0);
+    GoogleContactsPlugin(QObject *parent = nullptr);
     ~GoogleContactsPlugin();
 
 public Q_SLOTS: