Angular 6：HttpHeaders 无法在 Chrome 和 IE11 中读取 null 的属性“长度”（在 Firefox 中则不行）

在我的Angular6应用程序，我正在使用Http客户端将一些标头注入到我的 htpp 调用中以从我的后端服务器获取数据：

我的服务：

@Injectable()
export class LoadUserInfosService {

  public _headers = new HttpHeaders().set('Content-Type', 'application/json');

  constructor(private httpClient: HttpClient) {}

  getUserPnsInfos(cuid): Observable<object> {
    const headers = this._headers.append('login', login);
    return this.httpClient.get(myBackUrl, {headers: headers});
  }
}

我订阅的组件：

loadUserInfosFromPns(login) {
    this.loadUserInfosService.getUserPnsInfos(login).subscribe(infos => {
      let receivedInfos: any;
        receivedPnsInfos = infos ;
        console.log(receivedPnsInfos);
        if (pnsInfos !== null && receivedPnsInfos.cuid === cuid ) {
        } else {
          this.router.navigate(['unauthorized'], {skipLocationChange: true});
        }
      },
      error => {
        console.log(error);
      });
  }

在 Chrome 或 IE11 上运行时，我收到一些引用我的请求标头的错误：

TypeError: Cannot read property 'length' of null
    at HttpHeaders.push../node_modules/@angular/common/fesm5/http.js.HttpHeaders.applyUpdate (http.js:199)
    at http.js:170
    at Array.forEach (<anonymous>)
    at HttpHeaders.push../node_modules/@angular/common/fesm5/http.js.HttpHeaders.init (http.js:170)
    at HttpHeaders.push../node_modules/@angular/common/fesm5/http.js.HttpHeaders.forEach (http.js:235)
    at Observable._subscribe (http.js:1445)
    at Observable.push../node_modules/rxjs/_esm5/internal/Observable.js.Observable.subscribe (Observable.js:161)
    at subscribeTo.js:21
    at subscribeToResult (subscribeToResult.js:6)
    at MergeMapSubscriber.push../node_modules/rxjs/_esm5/internal/operators/mergeMap.js.MergeMapSubscriber._innerSub (mergeMap.js:127)

此错误仅出现在Chrome and IE11- 当在Firefox the 请求康复，但我没有得到

有什么想法、建议吗？

这可能是因为您在某些 http 请求中设置了未定义/空标头而引起的。