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

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