Why is JsonResponse not returning anything?

Question

symfony

I decided to add a couple of symfony components to codeigniter. I came across the fact that return new JsonResponse(['data' => rand(5, 100)]); does not work.
Who can tell why?

use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Request;

class Ajax extends Controller
{
    private $request;

    public function __construct()
    {
        header('Content-Type: application/json');
        $this->request = Request::createFromGlobals();
    }

    public function index()
    {
        return new JsonResponse(['data' => rand(5, 100)]);
    }