docs: def delete_activity(self, activity_id=None):
          """Deletes the Activity identified by the given Id.
  
          arg:    activityId (osid.id.Id): the Id of the Activity to
                  delete
          raise:  NotFound - an Activity was not found identified by the
                  given Id
          raise:  NullArgument - activityId is null
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          compliance: mandatory - This method must be implemented.
  
          """
          if activity_id is None:
              raise NullArgument()
          if not isinstance(activity_id, Id):
              raise InvalidArgument('argument type is not an osid Id')
  
          url_path = construct_url('activities',
                                   bank_id=self._catalog_idstr,
                                   act_id=activity_id)
          result = self._delete_request(url_path)
          return objects.Activity(result)