Laravel 5 - "Trying to get property of non-object"

Below I got my middleware that updates IP of the user.

namespace App\Http\Middleware;

use Closure;
use App\User;
use Illuminate\Support\Facades\Auth;
use Illuminate\Contracts\Auth\Guard;

class UserMiddleware
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function __construct(Guard $auth)
    {
         $this->auth = $auth;
    }
    public function handle($request, Closure $next)
    {
        User::where('id', $this->auth->user()->id)->update(['last_visit_ip' => '231']);
        return $next($request);
    }
}

Some notification is popping me up "Trying to get property of non-object" Any idea how to fix it?

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