QML: Special case null as binding type

This gives us the opportunity to map the JavaScript null to QVariant's
concept of isNull().

[ChangeLog][QML] Assigning JavaScript null to incompatibly typed
properties generates a compile error now, rather than a runtime error.

Fixes: QTBUG-72098
Change-Id: I72fd1c30d84128c774230eaaea10455b2a0e064c
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

2 files changed, 14 insertions, 0 deletions

diff --git a/tests/auto/qml/qqmlecmascript/data/qmlVarNullBinding.qml b/tests/auto/qml/qqmlecmascript/data/qmlVarNullBinding.qml
new file mode 100644
index 0000000000..6666b85ffd
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/qmlVarNullBinding.qml
@@ -0,0 +1,7 @@
+import QtQml 2.2
+
+QtObject {
+    property var foo: null
+    property bool signalSeen: false
+    onFooChanged: signalSeen = true
+}
diff --git a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
index 085cd5ffd0..e247ed4eff 100644
--- a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
+++ b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
@@ -5991,6 +5991,13 @@ void tst_qqmlecmascript::nullObjectInitializer()
         QVERIFY(value.userType() == qMetaTypeId<QObject*>());
         QVERIFY(!value.value<QObject*>());
     }
+
+    {
+        QQmlComponent component(&engine, testFileUrl("qmlVarNullBinding.qml"));
+        QScopedPointer<QObject> obj(component.create());
+        QVERIFY(!obj.isNull());
+        QVERIFY(!obj->property("signalSeen").toBool());
+    }
 }
 
 // Test that bindings don't evaluate once the engine has been destroyed