message: when instance-mode not exist in pika.conf, defalut is classic mode
diff: @@ -59,7 +59,7 @@ int PikaConf::Load()
  std::string instance_mode;
  GetConfStr("instance-mode", &instance_mode);
  - classic_mode_ = !strcasecmp(instance_mode.data(), "classic");
  + classic_mode_ = (instance_mode.empty() || !strcasecmp(instance_mode.data(), "classic"));
  if (classic_mode_) {
  std::vector<std::string> db_list;
  