diff --git a/autotests/usermetadatawritertest.cpp b/autotests/usermetadatawritertest.cpp
--- a/autotests/usermetadatawritertest.cpp
+++ b/autotests/usermetadatawritertest.cpp
@@ -95,6 +95,13 @@
     QCOMPARE(md.attribute(QStringLiteral("test.attribute")), QStringLiteral("attribute"));
     md.setAttribute(QStringLiteral("test.attribute"), QString());
     QVERIFY(!md.hasAttribute(QStringLiteral("test.attribute")));
+
+    // Check for side effects of calling sequence
+    QVERIFY(!md.hasAttribute(QStringLiteral("test.check_contains")));
+    md.setAttribute(QStringLiteral("test.check_contains"), QStringLiteral("dummy"));
+    QVERIFY(md.hasAttribute(QStringLiteral("test.check_contains")));
+    md.setAttribute(QStringLiteral("test.check_contains"), QString());
+    QVERIFY(!md.hasAttribute(QStringLiteral("test.check_contains")));
 }
 
 void UserMetaDataWriterTest::cleanupTestCase()
diff --git a/src/xattr_p.h b/src/xattr_p.h
--- a/src/xattr_p.h
+++ b/src/xattr_p.h
@@ -82,10 +82,12 @@
     const ssize_t size = 0;
 #endif
 
+    if (!value) {
+        return size;
+    }
+
     if (size <= 0) {
-        if (value) {
-            value->clear();
-        }
+        value->clear();
         return size;
     }
 
@@ -106,7 +108,7 @@
     const ssize_t r = 0;
 #endif
 
-    if(value) *value = QString::fromUtf8(data);
+    *value = QString::fromUtf8(data);
     return r;
 }
 
@@ -218,17 +220,16 @@
     CloseHandle(hFile);
     return false;
 #else
-    k_getxattr(path, name, nullptr);
-    return (errno != ENOATTR);
+    auto ret = k_getxattr(path, name, nullptr);
+    return (ret >= 0);
 #endif
 }
 
 inline bool k_isSupported(const QString& path)
 {
-    QString value;
 #if defined(Q_OS_LINUX) || defined(Q_OS_MAC) || defined(Q_OS_FREEBSD) || defined(Q_OS_NETBSD)
-    k_getxattr(path, QStringLiteral("user.test"), &value);
-    return (errno != ENOTSUP);
+    auto ret = k_getxattr(path, QStringLiteral("user.test"), nullptr);
+    return (ret >= 0) || (errno != ENOTSUP);
 #elif defined(Q_OS_WIN)
     QFileInfo f(path);
     const QString drive = QString(f.absolutePath().left(2)) + QStringLiteral("\\");