Angular的Reactive Forms异步自定义验证器Observable仍处于ng-pending状态

如何解决Angular的Reactive Forms异步自定义验证器Observable仍处于ng-pending状态

我试图创建正在调用服务器的自定义验证器，服务器以Observable 的形式返回组列表，当我在该字段中输入值时，它仍然保持“ ng-pending” >

create-group.component.ts

  ngOnInit(): void {
    this.groupForm = new FormGroup({
      name: new FormControl(
        '',[Validators.required,Validators.minLength(5),Validators.maxLength(50)],this.isExist
      ),parent: new FormControl(undefined),})
  }

  isExist(control: AbstractControl): Observable<any | null> {
    return this.groupsSettingService.getAllGroups().pipe(
      debounceTime(500),map(groups => groups.map(group => {
        if (group.name.toLowerCase() === control.value.toLowerCase())
          return { isExist: true };
        else
          return null;
      })),first()
    );
  }