Once a UObject* is GC’d, it is automatically set to null
This is not true for a UObject * bare pointer, that doesn’t have the UPROPERTY decorator.
If you make it UPROPERTY then the UObject * will keep the object alive.
To have a pointer to an object, which does not by itself keep the object alive, and gets set to null when the object dies, you need a TWeakObjectPtr<>.