问Angular4:表单无效，尽管字段中没有错误(使用自定义验证)

EN

ngOnInit(): void {
    this.emailField = new FormControl('mail@mail.com', Validators.email);
    this.pw1 = new FormControl('', [this.passwordAreEqualValidator, Validators.minLength(2)]);
    this.pw2 = new FormControl('', this.passwordAreEqualValidator);
    this.pwOld = new FormControl('', this.notEmptyIfNewIsTouchedValidator);

    this.form = this.formBuilder.group({
      pw1: this.pw1,
      pw2: this.pw2,
      emailField: this.emailField,
      pwOld: this.pwOld
    });
  }

notEmptyIfNewIsTouchedValidator(control: FormControl) : ValidationErrors | null {
    if (control.dirty) {
      if (control.value === '') {
        return {
          oldPasswordEmpty: true
        }
      }

      const parent = control.parent,
            pw1 = parent.get('pw1'),
            pw2 = parent.get('pw2');

      // this will trigger nothing in template, this part is only
      // to mark form invalid if password was entered. passwordNew1
      // cannot be false by default as this is okay when you only
      // want to change your e-mail adress.
      if (pw1.value.length === 0) {
        pw1.setErrors({noPassword: true});
      } else {
        if (pw1.hasError('noPassword')) {
          let pw1Errors = pw1.errors;
          delete pw1Errors.noPassword;  
          pw1.setErrors(pw1Errors);
        }
      }

      console.log('pw1 errors: ', pw1.errors);
      console.log('pw2 errors: ', pw2.errors);
      console.log('old errors: ', control.errors);
    }

    return null;
  }

  passwordAreEqualValidator(control: FormControl): ValidationErrors | null {
    if (control.dirty) {
      const
        parent = control.parent,
        pwOld = parent.get('pwOld'),
        pw1 = parent.get('pw1'),
        pw2 = parent.get('pw2');

      if (pwOld.value === '') {
        pwOld.setErrors({oldPasswordEmpty: true})
      }

      if (pw1.value !== pw2.value) {
        return {
          notEqual: true
        };
      } else {
        let pw1Errors = pw1.errors;

        if (pw1.hasError('notEqual')) {
          delete pw1Errors.notEqual;
          pw1.setErrors(pw1Errors);
        }

        if (pw1.hasError('noPassword')) {
          delete pw1Errors.noPassword;
          pw1.setErrors(pw1Errors);
        }

        pw2.setErrors(null);

        console.log('pw1 errors: ', pw1.errors);
        console.log('pw2 errors: ', pw2.errors);
        console.log('old errors: ', pwOld.errors);
      }
    }

    return null;
  }