apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/controller/ConfigController.java/ConfigController/namespaceBelongsToAppId
class ConfigController:  private boolean namespaceBelongsToAppId(String appId, String namespaceName) {
    //Every app has an 'application' namespace
    if (Objects.equals(ConfigConsts.NAMESPACE_APPLICATION, namespaceName)) {
      return true;
    }

    //if no appId is present, then no other namespace belongs to it
    if (ConfigConsts.NO_APPID_PLACEHOLDER.equalsIgnoreCase(appId)) {
      return false;
    }

    AppNamespace appNamespace = appNamespaceService.findByAppIdAndNamespace(appId, namespaceName);

    return appNamespace != null;
  }