angular Validators.compose问题

Question

您好我试图学习角度，当我尝试使用验证器时我得到错误，我收到错误： 无法读取null的属性'value'

这是我的组件：

import {Component} from 'angular2/core';
import {ControlGroup , Control, Validators, FormBuilder} from 'angular2/common';
import {CustomValidators} from './custom.validators4';

@Component({
selector    :   'contact',
templateUrl :   'app/form.template4.html'
})

export class FormComponent4{
form1 : ControlGroup;

constructor(fb : FormBuilder){
    this.form1 = fb.group({
        oldpass : ['', Validators.required],
        newpass : ['', Validators.required],
        repass  : ['', Validators.compose([ Validators.required , CustomValidators.retypeMatch ])]
    });
}



onSubmit(){
    this.form1.find('oldpass').setErrors({
        incorrect : true
    })
}
}

以下是我的CustomValidators组件：

import {ControlGroup} from 'angular2/common';

export class CustomValidators{

static retypeMatch(group : ControlGroup){

    var pass = group.find('newpass').value;
    var retype = group.find('repass').value;

    if(pass == '' || retype == '')
        return null;

    if(pass != retype)
        return {retypeMatch : true};

    return null;
}

}