Do not initialize class-type properties using default strings

lib/introspector.cpp

@@ -1019,7 +1019,8 @@ Property *Introspector::introspectProperty(const QString& id, const QVariantMap&
 
     // Apply default value (but not for unions)
     bool isUnion = (dynamic_cast<UnionType*>(baseType) != nullptr);
-    if (data.contains("default") && !isUnion) {
+    bool isClass = (dynamic_cast<Class*>(baseType) != nullptr);
+    if (data.contains("default") && !isUnion && !isClass) {
         // Quote anything but numbers and ints
         member->setDefaultValue(quoteValue(data.value("default").toString(), baseType));
     }