From 04350f5129a436c16e023dc54c01586cd5dbb3e4 Mon Sep 17 00:00:00 2001
From: Fabian Kosmale <fabian.kosmale@qt.io>
Date: Tue, 16 Feb 2021 15:49:37 +0100
Subject: QQmlPropertyPrivate::signalExpression: handle object being null

QQmlData::get expects a non-null pointer, therefore we need to check
whether the object still exists.

Note that while this fixes the crash in the referenced bug,
PropertyChanges still does not support a dynamic target.

Task-number: QTBUG-46350
Change-Id: Ifeecf5df83e87468a1d314ce2b120006124d6f4b
Reviewed-by: Maximilian Goldstein <max.goldstein@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit 1ff376e64bf5af6df7e0079700d2b9164037dc89)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/qml/qml/qqmlproperty.cpp                     |  4 ++++
 tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/src/qml/qml/qqmlproperty.cpp b/src/qml/qml/qqmlproperty.cpp
index 8f6639adf5..238a0462f0 100644
--- a/src/qml/qml/qqmlproperty.cpp
+++ b/src/qml/qml/qqmlproperty.cpp
@@ -925,6 +925,8 @@ QQmlPropertyPrivate::signalExpression(const QQmlProperty &that)
     if (!(that.type() & QQmlProperty::SignalProperty))
         return nullptr;
 
+    if (!that.d->object)
+        return nullptr;
     QQmlData *data = QQmlData::get(that.d->object);
     if (!data)
         return nullptr;
@@ -964,6 +966,8 @@ void QQmlPropertyPrivate::takeSignalExpression(const QQmlProperty &that,
         return;
     }
 
+    if (!that.d->object)
+        return;
     QQmlData *data = QQmlData::get(that.d->object, nullptr != expr);
     if (!data)
         return;
diff --git a/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp b/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
index 7177089d7c..4968d4e97f 100644
--- a/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
+++ b/tests/auto/qml/qqmlproperty/tst_qqmlproperty.cpp
@@ -195,6 +195,8 @@ private slots:
     void nestedQQmlPropertyMap();
 
     void underscorePropertyChangeHandler();
+
+    void signalExpressionWithoutObject();
 private:
     QQmlEngine engine;
 };
@@ -2263,6 +2265,14 @@ void tst_qqmlproperty::underscorePropertyChangeHandler()
     QVERIFY(changeHandler.isSignalProperty());
 }
 
+void tst_qqmlproperty::signalExpressionWithoutObject()
+{
+    QQmlProperty invalid;
+    QQmlPropertyPrivate::setSignalExpression(invalid, nullptr);
+    QQmlBoundSignalExpression *expr = QQmlPropertyPrivate::signalExpression(invalid);
+    QVERIFY(!expr);
+}
+
 QTEST_MAIN(tst_qqmlproperty)
 
 #include "tst_qqmlproperty.moc"
-- 
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