code: def get_root_objectives(self):
          
          # Implemented from template for
          # osid.ontology.SubjectHierarchySession.get_root_subjects_template
          root_ids = self._hierarchy_session.get_roots()
          collection = JSONClientValidated('learning',
                                           collection='Objective',
                                           runtime=self._runtime)
          result = collection.find(
              dict({'_id': {'$in': [ObjectId(root_id.get_identifier()) for root_id in root_ids]}},
                   **self._view_filter()))
          return objects.ObjectiveList(
              result,
              runtime=self._runtime,
              proxy=self._proxy)
docs: Gets the root objective in this objective hierarchy.
  
          return: (osid.learning.ObjectiveList) - the root objective
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method is must be implemented.*