def get_objective_notification_session(self, objective_receiver, proxy):
raise Unimplemented()<EOL>
Gets the notification session for notifications pertaining to objective changes.

        :param objective_receiver: the objective receiver
        :type objective_receiver: ``osid.learning.ObjectiveReceiver``
        :param proxy: a proxy
        :type proxy: ``osid.proxy.Proxy``
        :return: an ``ObjectiveNotificationSession``
        :rtype: ``osid.learning.ObjectiveNotificationSession``
        :raise: ``NullArgument`` -- ``objective_receiver`` or ``proxy`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_objective_notification()`` is ``false``

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