Fix nullptr handling in binding

Fixes: QTBUG-77027
Change-Id: I61d5a20329ffe95af810b89e338eee2bc10bfe04
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

2 files changed, 39 insertions, 0 deletions

diff --git a/tests/auto/qml/qqmlproperty/data/nullPropertyBinding.qml b/tests/auto/qml/qqmlproperty/data/nullPropertyBinding.qml
new file mode 100644
index 0000000000..4fffc7aead
--- /dev/null
+++ b/tests/auto/qml/qqmlproperty/data/nullPropertyBinding.qml
@@ -0,0 +1,22 @@
+import QtQuick 2.12
+
+Item {
+    id: root
+
+    width: 640
+    height: 480
+
+    property bool toggle: false
+    property Item bound
+    property string message: "defined"
+
+    readonly property Item item: root.toggle ? root : null
+
+    Binding { target: root; property: "bound"; value: item}
+
+    function tog() {
+        console.info(root.bound ? root.bound.message: "undefined")
+        root.toggle = !root.toggle
+        return 42;
+    }
+}
diff --git a/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp b/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
index 04c61ec11b..67da768f73 100644
--- a/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
+++ b/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
@@ -144,6 +144,7 @@ private slots:
     void deeplyNestedObject();
     void readOnlyDynamicProperties();
     void aliasToIdWithMatchingQmlFileNameOnCaseInsensitiveFileSystem();
+    void nullPropertyBinding();
 
     void floatToStringPrecision_data();
     void floatToStringPrecision();
@@ -2059,6 +2060,22 @@ void tst_qqmlproperty::aliasToIdWithMatchingQmlFileNameOnCaseInsensitiveFileSyst
     QVERIFY(property.isValid());
 }
 
+// QTBUG-77027
+void tst_qqmlproperty::nullPropertyBinding()
+{
+    const QUrl url = testFileUrl("nullPropertyBinding.qml");
+    QQmlEngine engine;
+    QQmlComponent component(&engine, url);
+    QScopedPointer<QObject> root(component.create());
+    QVERIFY(root);
+    QTest::ignoreMessage(QtMsgType::QtInfoMsg, "undefined");
+    QMetaObject::invokeMethod(root.get(), "tog");
+    QTest::ignoreMessage(QtMsgType::QtInfoMsg, "defined");
+    QMetaObject::invokeMethod(root.get(), "tog");
+    QTest::ignoreMessage(QtMsgType::QtInfoMsg, "undefined");
+    QMetaObject::invokeMethod(root.get(), "tog");
+}
+
 void tst_qqmlproperty::floatToStringPrecision_data()
 {
     QTest::addColumn<QString>("propertyName");