@abc.abstractmethod<EOL><INDENT>def get_grade_system_notification_session(self, grade_system_receiver):<DEDENT>
return<EOL>
Gets the notification session for notifications pertaining to grade system changes.

        :param grade_system_receiver: the grade system receiver
        :type grade_system_receiver: ``osid.grading.GradeSystemReceiver``
        :return: a ``GradeSystemNotificationSession``
        :rtype: ``osid.grading.GradeSystemNotificationSession``
        :raise: ``NullArgument`` -- ``grade_system_receiver`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_grade_system_notification()`` is ``false``

        *compliance: optional -- This method must be implemented if
        ``supports_grade_system_notification()`` is ``true``.*