code: def get_vault_hierarchy_design_session(self):
          
          if not self.supports_vault_hierarchy_design():
              raise errors.Unimplemented()
          # pylint: disable=no-member
          return sessions.VaultHierarchyDesignSession(runtime=self._runtime)
docs: Gets the session designing vault hierarchies.
  
          return: (osid.authorization.VaultHierarchyDesignSession) - a
                  ``VaultHierarchyDesignSession``
          raise:  OperationFailed - unable to complete request
          raise:  Unimplemented - ``supports_vault_hierarchy_design() is
                  false``
          *compliance: optional -- This method must be implemented if
          ``supports_vault_hierarchy_design()`` is true.*