apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/controller/NamespaceController.java/NamespaceController/findMissingNamespaces
class NamespaceController:  @GetMapping("/apps/{appId}/envs/{env}/clusters/{clusterName}/missing-namespaces")
  public MultiResponseEntity<String> findMissingNamespaces(@PathVariable String appId, @PathVariable String env, @PathVariable String clusterName) {

    MultiResponseEntity<String> response = MultiResponseEntity.ok();

    Set<String> missingNamespaces = findMissingNamespaceNames(appId, env, clusterName);

    for (String missingNamespace : missingNamespaces) {
      response.addResponseEntity(RichResponseEntity.ok(missingNamespace));
    }

    return response;
  }