code: def get_relationships_by_genus_type(self, relationship_genus_type=None):
          
          if relationship_genus_type is None:
              raise NullArgument()
          url_path = ('/handcar/services/relationship/families/' +
                      self._catalog_idstr + '/relationships?genustypeid=' +
                      relationship_genus_type.get_identifier())
          return objects.RelationshipList(self._get_request(url_path))
docs: Gets a ``RelationshipList`` corresponding to the given relationship genus ``Type``
              which does not include relationships of types derived from the specified ``Type``.
  
          arg:    relationship_genus_type (osid.type.Type): a relationship
                  genus type
          return: (osid.relationship.RelationshipList) - the returned
                  ``Relationship list``
          raise:  NullArgument - ``relationship_genus_type`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method must be implemented.*