apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/service/NamespaceService.java/NamespaceService/findNamespaces
class NamespaceService:  public List<Namespace> findNamespaces(String appId, String clusterName) {
    List<Namespace> namespaces = namespaceRepository.findByAppIdAndClusterNameOrderByIdAsc(appId, clusterName);
    if (namespaces == null) {
      return Collections.emptyList();
    }
    return namespaces;
  }