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>`

def get_relation_type(self, relation):
        """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>`
        """
        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)