Gets a composiiton administrative session for the given
        repository.

        arg:    repository_id (osid.id.Id): the Id of the repository
        return: (osid.repository.CompositionAdminSession) - a
                CompositionAdminSession
        raise:  NotFound - repository_id not found
        raise:  NullArgument - repository_id is null
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_composition_admin() or
                supports_visible_federation() is false
        compliance: optional - This method must be implemented if
                    supports_composition_admin() and
                    supports_visible_federation() are true.

def get_composition_admin_session_for_repository(self, repository_id=None):
        """Gets a composiiton administrative session for the given
        repository.

        arg:    repository_id (osid.id.Id): the Id of the repository
        return: (osid.repository.CompositionAdminSession) - a
                CompositionAdminSession
        raise:  NotFound - repository_id not found
        raise:  NullArgument - repository_id is null
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_composition_admin() or
                supports_visible_federation() is false
        compliance: optional - This method must be implemented if
                    supports_composition_admin() and
                    supports_visible_federation() are true.

        """
        if repository_id is None:
            raise NullArgument()
        if not self.supports_composition_admin() or not self.supports_visible_federation():
            raise Unimplemented()
        try:
            from . import sessions
        except ImportError:
            raise  # OperationFailed()
        try:
            session = sessions.CompositionSearchSession(repository_id,
                                                        proxy=self._proxy,
                                                        runtime=self._runtime)
        except AttributeError:
            raise  # OperationFailed()
        return session