Laravel Constructor session work

 public function __construct()
    {
        $this->middleware(function ($request, $next) {
            //dd(session()->get('logged_in'));
            if(session()->get('logged_in') == NULL)
            {
                session()->flash('flash-danger', 'Please login with your username and password');
                return redirect('admin/login');
            }else{
                return $next($request);
            }
        });
    }