Gets the notification session for subscribing to changes to a
        repository.

        arg:    repository_receiver
                (osid.repository.RepositoryReceiver): the notification
                callback
        arg     proxy (osid.proxy.Proxy): a proxy
        return: (osid.repository.RepositoryNotificationSession) - a
                RepositoryNotificationSession
        raise:  NullArgument - repository_receiver is null
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_repository_notification() is
                false
        compliance: optional - This method must be implemented if
                    supports_repository_notification() is true.

def get_repository_notification_session(self, repository_receiver, proxy):
        """Gets the notification session for subscribing to changes to a
        repository.

        arg:    repository_receiver
                (osid.repository.RepositoryReceiver): the notification
                callback
        arg     proxy (osid.proxy.Proxy): a proxy
        return: (osid.repository.RepositoryNotificationSession) - a
                RepositoryNotificationSession
        raise:  NullArgument - repository_receiver is null
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented - supports_repository_notification() is
                false
        compliance: optional - This method must be implemented if
                    supports_repository_notification() is true.

        """
        if repository_receiver is None:
            raise NullArgument()
        if not self.supports_repository_notification():
            raise Unimplemented()
        try:
            from . import sessions
        except ImportError:
            raise  # OperationFailed()
        proxy = self._convert_proxy(proxy)
        try:
            session = sessions.RepositoryNotificationSession(repository_receiver, proxy, runtime=self._runtime)
        except AttributeError:
            raise  # OperationFailed()
        return session