code: def get_objective_bank_hierarchy_design_session(self):
          
          if not self.supports_objective_bank_hierarchy_design():
              raise errors.Unimplemented()
          # pylint: disable=no-member
          return sessions.ObjectiveBankHierarchyDesignSession(runtime=self._runtime)
docs: Gets the session designing objective bank hierarchies.
  
          return: (osid.learning.ObjectiveBankHierarchyDesignSession) - an
                  ``ObjectiveBankHierarchyDesignSession``
          raise:  OperationFailed - unable to complete request
          raise:  Unimplemented -
                  ``supports_objective_bank_hierarchy_design() is false``
          *compliance: optional -- This method must be implemented if
          ``supports_objective_bank_hierarchy_design()`` is true.*