在我的角度應用程序中，我想添加一些帶有 firebase 的網絡推送通知。import { Component } from "@angular/core";import { AngularFireMessaging } from "@angular/fire/messaging";import { mergeMapTo } from "rxjs/operators";@Component({  selector: "app-home",  templateUrl: "home.page.html",  styleUrls: ["home.page.scss"],})export class HomePage {  constructor(private afMessaging: AngularFireMessaging) {}  requestPermission() {    this.afMessaging.requestPermission      .pipe(mergeMapTo(this.afMessaging.tokenChanges))      .subscribe(        (token) => {          console.log("Permission granted! Save to the server!", token);          this.afMessaging.messages.subscribe(            (message) => {              console.log(message);            },            (error) => {              console.log("error", error);            }          );        },        (error) => {          console.error(error);        }      );  }}當我通過 Firebase 發送測試消息時，我可以獲得一個令牌，并且在應用程序下的開發者控制臺中是通知請求。但是在我的控制臺中，我收到了這個錯誤：zone-evergreen.js:659 Unhandled Promise rejection: this._next is not a function ; Zone: <root> ; Task: ServiceWorkerContainer.addEventListener:message ; Value: TypeError: this._next is not a function    at WindowController.next [as onMessageCallback] (Subscriber.js:49)    at WindowController.<anonymous> (index.esm.js:1067)    at step (tslib.es6.js:100)    at Object.next (tslib.es6.js:81)    at tslib.es6.js:74    at new ZoneAwarePromise (zone-evergreen.js:960)    at __awaiter (tslib.es6.js:70)    at WindowController.push../node_modules/@firebase/messaging/dist/index.esm.js.WindowController.messageEventListener (index.esm.js:1056)    at ServiceWorkerContainer.<anonymous> (index.esm.js:890)    at ZoneDelegate.invokeTask (zone-evergreen.js:399) TypeError: this._next is not a function我正在使用 Angular 9 和 angular/fire 和 firebase。