L5.5 路由如何组合 group namespace middleware prefix ？

Route::middleware('CheckAdminLogin')->prefix('dashboard')->namespace('Dashboard')->group(function () {

    Route::any('/', 'IndexController@index')->name('dashboard.index'); //首页
    Route::any('/login', 'IndexController@login')->name('dashboard.login'); //登陆
    Route::any('/logout', 'IndexController@logout')->name('dashboard.logout'); //退出登录

});

这样写总是提示我：ErrorException thrown with message "Trying to get property of non-object"

我写了个 CheckAdminLogin.php 在 App\Http\Middleware 下，内容如下：

namespace App\Http\Middleware;

use Closure;
use Illuminate\Http\Request;

class CheckAdminLogin
{

    protected $except = [
        '/dashboard/login'
    ];

    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle(Request $request, Closure $next)
    {
        if(!$request->session()->has('admin_id') ||  !$request->session()->has('allow_login') &&  $request->session()->get('allow_login') == 1) {
            return route('dashboard.login').'?return_url='.$request->fullUrl();
        }

        return $next($request);
    }    

}

并且在 Kernel.php 中的 $routeMiddleware 中注册：

'CheckAdminLogin' => \App\Http\Middleware\CheckAdminLogin::class,

刚刚接触laravel的小白，请多指教。