Angular 2 Typescript：TypeError：this.validator 不是函数

我正在用ControlGroup构建一个表单，并在其中加载一个类对象.然而，我有一半的时间遇到了标题中提到的错误.有些表单确实加载，有些则不加载.

我有一个这样的类文件:

export class User {
    id: number;
    email: string;
    sign_in_count: number;
    created_at: string;
    first_name: string;
    last_name: string;
    birth_date: Date;
    news_letter: boolean;
    fb_id: string;
    gender: boolean;
    phone: string;
    picture: any;
}

在我的类中加载UserDetaili控件:

export class UserDetailComponent implements OnInit {
    user: User;
    userDetailForm: ControlGroup;

    constructor(
        private form: FormBuilder,
        private _userService: UserService,
        private _router: Router,
        private params: RouteSegment
    ) { }
    ngOnInit() {
        this.user = this._userService.getUser();
        if (this.user === undefined) {
            this._userService.getSingleUser(this.params.getParam('id'))
                .subscribe(data => (this.user = data, this.setForm()));
        } else {
            this.setForm();
        }
    }

    setForm() {
        this.userDetailForm = this.form.group(this.user);
    }
}

在最后一行，我得到了下面的stacktrace错误:

browser_adapter.ts:78 TypeError: this.validator is not a function
    at Control.AbstractControl._runValidator (model.ts:146)
    at Control.AbstractControl.updateValueAndValidity (model.ts:128)
    at new Control (model.ts:282)
    at FormBuilder.control (form_builder.ts:32)
    at FormBuilder._createControl (form_builder.ts:66)
    at eval (form_builder.ts:50)
    at Function.StringMapWrapper.forEach (collection.ts:132)
    at FormBuilder._reduceControls (form_builder.ts:49)
    at FormBuilder.group (form_builder.ts:19)
    at UserDetailComponent.setForm (user-detail.component.ts:95)