Angular 8应用程序编译显示：“错误TS1005：'：'预期”

嗨，我正在通过观看教程来开发Angle 8应用程序，在标头组件中，我想要当前登录用户的电子邮件ID。我的auth.service.ts如下所示：

import { Injectable } from "@angular/core";

import { AngularFireAuth } from "@angular/fire/auth";

@Injectable({
  providedIn: "root",
})
export class AuthService {
  constructor(private auth: AngularFireAuth) {}

  signUp(email: string, password: string) {
    return this.auth.auth.createUserWithEmailAndPassword(email, password);
  }

  signIn(email: string, password: string) {
    return this.auth.auth.signInWithEmailAndPassword(email, password);
  }

  getUser() {
    return this.auth.authState;
  }
  signOut() {
    return this.auth.auth.signOut();
  }
}

我的header.component.ts是：

import { Component, OnInit } from "@angular/core";
import { AuthService } from "src/app/services/auth.service";
import { ToastrService } from "ngx-toastr";
import { Router } from "@angular/router";

@Component({
  selector: "app-header",
  templateUrl: "./header.component.html",
  styleUrls: ["./header.component.css"],
})
export class HeaderComponent implements OnInit {
  email:string = null;
  constructor(
    private auth: AuthService,
    private router: Router,
    private toastr: ToastrService
  ) {
    auth.getUser().subscribe((user)=>{
      console.log("User is:",user);
      this.email = user?.email;
    })
  }

  ngOnInit() {}

  async handSignOut(){
    try {
      await this.auth.signOut();
      this.router.navigateByUrl("/signin");
      this.toastr.info("Logout sucess");
      this.email = null;
    } catch (error) {
      this.toastr.error("Problem in Signout");
      
    }
  }
}

当我编译代码时，它显示：

ERROR in src/app/layout/header/header.component.ts:20:25 - error TS1109: Expression expected.

20       this.email = user?.email;
                           ~
src/app/layout/header/header.component.ts:20:31 - error TS1005: ':' expected.

20       this.email = user?.email;
                                 ~

当我删除“？” 内联：this.email = user？.email; 它编译成功。我该如何解决这个问题？

我的package.json：

{
  "name": "travelgram",
  "version": "0.0.0",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "~8.2.7",
    "@angular/common": "~8.2.7",
    "@angular/compiler": "~8.2.7",
    "@angular/core": "~8.2.7",
    "@angular/fire": "^5.4.2",
    "@angular/forms": "~8.2.7",
    "@angular/platform-browser": "~8.2.7",
    "@angular/platform-browser-dynamic": "~8.2.7",
    "@angular/router": "~8.2.7",
    "@fortawesome/angular-fontawesome": "^0.6.1",
    "@fortawesome/fontawesome-svg-core": "^1.2.29",
    "bootstrap": "^4.5.0",
    "browser-image-resizer": "^2.1.0",
    "firebase": "^7.15.4",
    "ngx-toastr": "^10.1.0",
    "rxjs": "~6.4.0",
    "tslib": "^1.10.0",
    "uuid": "^8.2.0",
    "zone.js": "~0.9.1"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "~0.803.5",
    "@angular/cli": "~8.3.5",
    "@angular/compiler-cli": "~8.2.7",
    "@angular/language-service": "~8.2.7",
    "@types/node": "~8.9.4",
    "@types/jasmine": "~3.3.8",
    "@types/jasminewd2": "~2.0.3",
    "codelyzer": "^5.0.0",
    "jasmine-core": "~3.4.0",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~4.1.0",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "~2.0.1",
    "karma-jasmine": "~2.0.1",
    "karma-jasmine-html-reporter": "^1.4.0",
    "protractor": "~5.4.0",
    "ts-node": "~7.0.0",
    "tslint": "~5.15.0",
    "typescript": "~3.5.3",
    "@angular-devkit/architect": "<0.900 || ^0.900.0-0 || ^9.0.0-0",
    "firebase-tools": "^7.12.0",
    "fuzzy": "^0.1.3",
    "inquirer": "^6.2.2",
    "inquirer-autocomplete-prompt": "^1.0.1"
  }
}