private Packet joinToGame(Packet packet) {
        
        if(nickname == null) {
            return Packet.getUserNotSingingUpPacket();
        }
        
        Integer ID = (Integer) packet.getData();
        
        switch(controller.getLobbyController().joinToLobby(ID, this)) {
            case LobbyController.OK_OPT:
                return null;
            case LobbyController.NOT_EXIST_OPT:
                return Packet.getGameNotExistPacket();
            case LobbyController.FULL_OPT:
                return Packet.getGameIsFullPacket();
        }
        
        return Packet.getServerErrorPacket();        
    }