def METHOD_NAME(self, name: str) -> Optional[Union["Model", Sequence["Model"]]]:
    """
    Returns the related model/models if relation is set.
    Actual call is delegated to Relation instance registered under relation name.
    :param name: name of the relation
    :type name: str
    :return: related model or list of related models if set
    :rtype: Optional[Union[Model, List[Model]]
    """
    relation = self._relations.METHOD_NAME(name, None)
    if relation is not None:
        return relation.METHOD_NAME()
    return None  # pragma nocover