apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/service/AppNamespaceService.java/AppNamespaceService/findOne
class AppNamespaceService:  public AppNamespace findOne(String appId, String namespaceName) {
    Preconditions
        .checkArgument(!StringUtils.isContainEmpty(appId, namespaceName), "appId or Namespace must not be null");
    return appNamespaceRepository.findByAppIdAndName(appId, namespaceName);
  }