错误处理 – RxJs如何在ReplaySubject中引发异常？

import * as localforage from "localforage";
import { ReplaySubject } from 'rxjs/ReplaySubject';

@Injectable()
export class CommentService {
    private localForage = require("localforage");

    addComment (myvalue: string): Observable<Comment[]> {
        var reply:ReplaySubject<any> = new ReplaySubject(1);
        localforage.setItem(that.key,that.elencoCommenti).then(function (value) {
            //throw new Error("Value cannot be 3");
            reply.throw(Error('Error2'));           
            //              reply.next( value );
            //              reply.complete();
        });
        return reply;
    }

}

该服务结合了提出异常的方法.
当我尝试订阅

submitComment(){
    // Variable to hold a reference of addComment
    let commentOperation:Observable<string>;

    commentOperation = this.commentService.addComment(this.model)

    // Subscribe to observable
    commentOperation.subscribe(
                            comments => {
                                console.log('ok:');
                                console.log(comments);
                            },err => {
                                // Log errors if any
                                console.log('error:');
                                console.log(err);
                            });
}

我没有收到错误.
如何在ReplaySubject中引发异常？