How to solve Call to a member function admin() on null error?

Question

Laravel

I'm making an admin page. Created middleware and registered check, added routes. But there is an error in validation: 'Call to a member function admin() on null'

public function handle(Request $request, Closure $next)
    {
        if(Auth::user()->admin()==0){
            return redirect()->route('index');
        }

        return $next($request);
    }

Route::get('/admin', [App\Http\Controllers\AdminController::class, 'admin'])->middleware('isadmin');

Answer 1

public function handle(Request $request, Closure $next)
{
  if (Auth::guest() || Auth::user()->admin()==0){
    return redirect()->route('index');
  }
  return $next($request);
}

Answer 2

It checks whether the user is an admin, but not the fact that the user is logged into his account. This case needs to be taken into account.