RPython cannot assure that the return of get_instance_invokable is not None
RPython cannot assure that the return of get_instance_invokable is not None

so we assist it that this is indeed the case;

smarr/PySOM,smarr/RTruffleSOM,SOM-st/RPySOM,SOM-st/RTruffleSOM,SOM-st/PySOM,SOM-st/RPySOM,SOM-st/RTruffleSOM,SOM-st/PySOM,smarr/RTruffleSOM,smarr/PySOM