def _apply_update_receiver(self, receiver, reply_id):
        """
        Updates `self.receiver` and/or `self.reply_id` if they still contain the default value.
        :param receiver: The receiver `chat_id` to use.
                         Either `self.receiver`, if set, e.g. when instancing `TextMessage(receiver=10001231231, ...)`,
                         or the `chat.id` of the update context, being the id of groups or the user's `from_peer.id` in private messages.
        :type  receiver: None | str|unicode | int


        :param reply_id: Reply to that `message_id` in the chat we send to.
                         Either `self.reply_id`, if set, e.g. when instancing `TextMessage(reply_id=123123, ...)`,
                         or the `message_id` of the update which triggered the bot's functions.
        :type  reply_id: DEFAULT_MESSAGE_ID | int
        """
        if self.receiver is None:
            self.receiver = receiver
        # end if
        if self.reply_id is DEFAULT_MESSAGE_ID:
            self.reply_id = reply_id