docs: def get_activities_for_objective(self, objective_id):
          """Gets the activities for the given objective.
  
          In plenary mode, the returned list contains all of the
          activities mapped to the objective ``Id`` or an error results if
          an Id in the supplied list is not found or inaccessible.
          Otherwise, inaccessible ``Activities`` may be omitted from the
          list and may present the elements in any order including
          returning a unique set.
  
          arg:    objective_id (osid.id.Id): ``Id`` of the ``Objective``
          return: (osid.learning.ActivityList) - list of enrollments
          raise:  NotFound - ``objective_id`` not found
          raise:  NullArgument - ``objective_id`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method is must be implemented.*
  
          """
          # Implemented from template for
          # osid.learning.ActivityLookupSession.get_activities_for_objective_template
          # NOTE: This implementation currently ignores plenary view
          collection = JSONClientValidated('learning',
                                           collection='Activity',
                                           runtime=self._runtime)
          result = collection.find(
              dict({'objectiveId': str(objective_id)},
                   **self._view_filter()))
          return objects.ActivityList(result, runtime=self._runtime)