ErrorBag is always empty in Laravel 5.2
As of v5.2.27, released on 2015-03-25, all routes in app\Http\routes.php are now in the web middleware group by default. If you have explicitly specified this middleware group inside your app\Http\routes.php file, you should remove it and that should resolve your issue.
In my case, I moved \Illuminate\Session\Middleware\StartSession::class from my web group to the $middleware array.