def get_objective_notification_session(self, objective_receiver=None):
raise Unimplemented()<EOL>
Gets the notification session for notifications pertaining to objective changes.

        arg:    objective_receiver (osid.learning.ObjectiveReceiver):
                the objective receiver
        return: (osid.learning.ObjectiveNotificationSession) - an
                ``ObjectiveNotificationSession``
        raise:  NullArgument - ``objective_receiver`` 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``.*