code: def get_relation_type(self, relation):
          
          route_values = {}
          if relation is not None:
              route_values['relation'] = self._serialize.url('relation', relation, 'str')
          response = self._send(http_method='GET',
                                location_id='f5d33bc9-5b49-4a3c-a9bd-f3cd46dd2165',
                                version='5.1-preview.2',
                                route_values=route_values)
          return self._deserialize('WorkItemRelationType', response)
docs: GetRelationType.
          [Preview API] Gets the work item relation type definition.
          :param str relation: The relation name
          :rtype: :class:`<WorkItemRelationType> <azure.devops.v5_1.work-item-tracking.models.WorkItemRelationType>`