def get_activity_notification_session(self, activity_receiver=None, proxy=None):
if proxy is None:<EOL><INDENT>raise NullArgument()<EOL><DEDENT>raise Unimplemented()<EOL>
Gets the notification session for notifications pertaining to activity changes.

        arg:    activity_receiver (osid.learning.ActivityReceiver): the
                activity receiver
        arg:    proxy (osid.proxy.Proxy): a proxy
        return: (osid.learning.ActivityNotificationSession) - an
                ``ActivityNotificationSession``
        raise:  NullArgument - ``activity_receiver`` or ``proxy`` is
                ``null``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - ``supports_activity_notification()`` is
                ``false``
        *compliance: optional -- This method must be implemented if
        ``supports_activity_notification()`` is ``true``.*