Return a list of non-primitive types used by this object.

def _get_type_list(self, props):
        """Return a list of non-primitive types used by this object."""
        type_list = []
        for k, v in list(props.items()):
            t = self._get_property_type(v)
            if t is not None:
                type_list.append(t)
        return sorted(type_list)