@utilities.remove_null_proxy_kwarg<EOL><INDENT>def get_objective_hierarchy_session(self):<DEDENT>
if not self.supports_objective_hierarchy():<EOL><INDENT>raise errors.Unimplemented()<EOL><DEDENT>return sessions.ObjectiveHierarchySession(runtime=self._runtime)<EOL>
Gets the session for traversing objective hierarchies.

        return: (osid.learning.ObjectiveHierarchySession) - an
                ``ObjectiveHierarchySession``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - ``supports_objective_hierarchy()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_objective_hierarchy()`` is ``true``.*