generic type subject<t>需要1个类型参数。-角度

export class RItemComponent implements OnInit {

  apiPath = environment.apiUrl;
  private ngUnsubscribe: Subject = new Subject();

  constructor(private _sharedService: SharedService) { }

  rItems: Product[];

  ngOnInit() {
    this._sharedService.
      getReceiptItem().takeUntil(this.ngUnsubscribe).
      subscribe(products => this.rItems = products);
  }

  ngOnDestroy() {
    this.ngUnsubscribe.next();
    this.ngUnsubscribe.complete();
  }
}

但现在我有一个错误:

我不明白为什么?