Undefined Offset: 1 in Laravel 5 Due to Middleware

I'm Getting this error with the route add-site.

ErrorException in compiled.php line 7315: Undefined Offset: 1

Here are the files...

routes.php

Route::get('add-site',['middleware' => 'auth',function()
{
    return view('dashboard.add_site');
}]);

Middleware

public function handle($request, Closure $next)
{
    if(Session::has('sa_loggedin')==FALSE and !Session::has('sa_server_id'))
    {
        return "error!";
    }
    else
    {
        return $next($request);
    }

    return 0;
}

I know the error might be silly but I'm not getting it... I'm trying to solve this error since hours...

via Chebli Mohamed