@utilities.remove_null_proxy_kwarg<EOL><INDENT>def get_repository_hierarchy_session(self):<DEDENT>
if not self.supports_repository_hierarchy():<EOL><INDENT>raise errors.Unimplemented()<EOL><DEDENT>return sessions.RepositoryHierarchySession(runtime=self._runtime)<EOL>
Gets the repository hierarchy traversal session.

        return: (osid.repository.RepositoryHierarchySession) - ``a
                RepositoryHierarchySession``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - ``supports_repository_hierarchy()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_repository_hierarchy()`` is ``true``.*