无法读取 null 的属性“outlet”

我有下一个问题：Cannot read property 'outlets' of null。我的项目可以工作，但一段时间后它停止工作，但我没有更改我的代码。请帮帮我。
Update
我的带有路由器插座的组件：

import { Component } from '@angular/core';

@Component({
  selector: 'app',
  template: '
    <nav-menu></nav-menu>
    <router-outlet></router-outlet>
    <footer-component></footer-component>

',
})
export class AppComponent  {}

应用程序模块：

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { RouterModule } from '@angular/router';
import { LocationStrategy, PathLocationStrategy, APP_BASE_HREF } from       '@angular/common';
import { HttpModule } from '@angular/http';
import {FormsModule,ReactiveFormsModule} from '@angular/forms';
//+components
@NgModule({
    imports:
    [
        BrowserModule,
        HttpModule,
        FormsModule,
        ReactiveFormsModule,
        RouterModule.forRoot([
            { path: '', component: HomeComponent },
            { path: 'home', component: HomeComponent },
            { path: 'blog', component: BlogComponent },
            { path: '2016/:link', component: BlogArticleFullComponent },
            {
                path: 'admin', component: AdminComponent, 
                children: [
                    { path: 'new', component: NewArticleComponent },
                    { path: 'new-writer', component: NewWriterComponent },
                    { path: 'new-tag', component: NewTagComponent }
                ] },
            { path: '**', redirectTo: '', pathMatch: 'full'}
        ])
    ],
    declarations:
    [//components
    ],
    bootstrap:
    [
        AppComponent
    ],
    providers:
    [
        { provide: APP_BASE_HREF, useValue: '/' },
        { provide: LocationStrategy, useClass: PathLocationStrategy }
    ]
})
export class AppModule { }

附：有'对'的引用，因为 stackoverflow ``-是代码。

供将来参考：我在使用时遇到此错误[routerLink]一个数组看起来像['/foo', null]。通过提供一个对象而不是null.