add null check for qmlRegisterSingletonType()

When the callback passed to the function returns nullptr,
QQmlData::ensurePropertyCache(e, o) crashes.

Change-Id: I11efd7e9d6c5f18611e796d896384dd14a280303
Reviewed-by: Michael Brasser <michael.brasser@live.com>
Reviewed-by: Christopher Adams <chris.adams@jollamobile.com>
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlmetatype.cpp b/src/qml/qml/qqmlmetatype.cpp
index 41d44a821a..cb8c2bd3b5 100644
--- a/src/qml/qml/qqmlmetatype.cpp
+++ b/src/qml/qml/qqmlmetatype.cpp
@@ -225,6 +225,9 @@ void QQmlType::SingletonInstanceInfo::init(QQmlEngine *e)
         v4->pushGlobalContext();
         QObject *o = qobjectCallback(e, e);
         setQObjectApi(e, o);
+        if (!o) {
+            qFatal("qmlRegisterSingletonType(): \"%s\" is not available because the callback function returns a null pointer.", qPrintable(typeName));
+        }
         // if this object can use a property cache, create it now
         QQmlData::ensurePropertyCache(e, o);
         v4->popContext();