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

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

    for (String missingNamespace : missingNamespaces) {
      namespaceAPI.createMissingAppNamespace(Env.valueOf(env), findAppNamespace(appId, missingNamespace));
    }

    return ResponseEntity.ok().build();
  }