检索图标时出错：无法读取属性＆＃39;令牌＆＃39;为null

Question

我已经实现了mat图标注册表服务，这使得SVG图标可以用于材料中的mat-icon标记。最初它正在工作，但突然出现此错误，无法检索任何图标。

我的图标服务

import { DomSanitizer } from "@angular/platform-browser";
import { MatIconRegistry } from "@angular/material/icon";
import { Injectable } from "@angular/core";

@Injectable({
  providedIn: 'root'
})
export class IconService {

  public icons = [
    'email',
    'facebook',
    ....
  ];
  constructor(
    private matIconRegistry: MatIconRegistry,
    private domSanitizer: DomSanitizer
  ) {}
  init() {
    for (let icon of this.icons){
      this.matIconRegistry.addSvgIcon(
        icon,
        this.domSanitizer.bypassSecurityTrustResourceUrl('../../../../assets/fonts/'+ icon +'.svg')
      );
    }
  }
}

应用组件

import { Component, OnInit } from '@angular/core';
import { IconService } from './layout/services/icon/icon.service';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss']
})
export class AppComponent implements OnInit {

  constructor(
    public iconService: IconService,
  ) {}

  ngOnInit(): void {
    this.iconService.init();
  }

}