Form Request Validation returns empty error messages – Laravel 5.3

I've got a problem with error messages during validation in Laravel. I've got my custom Request:

class CreateCv extends Request
{
    public function authorize()
    {
        return true;
    }

    public function rules()
    {
        return [
            'name' => 'required',
            'surname' => 'required',
        ];
    }

    public function messages()
    {
        return [
            'name.required' => 'Fill the name!',
            'surname.required'  => 'Fill the surname!',
        ];
    }
}

and then I've got a controller with create method:

class CvController extends Controller
{

    public function create(Requests\CreateCv $request) {
        return response()->json(['ok' => true], 200);
    }
}

If everything is filled up, then it returns json response "ok" : true correctly. But when something is missing, then it returns empty msg: "msg": "". What causes this problem?

via user3216673