Symfony唯一实体错误消息不显示

use Symfony\Component\Validator\Constraints as Assert;

class MyEntity
{
    /**
     * @Assert\NotBlank()
     * @Assert\Unique(message="该字段值已存在")
     */
    private $uniqueField;
    
    // ...
}

use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\OptionsResolver\OptionsResolver;

class MyEntityType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('uniqueField', TextType::class);
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'data_class' => MyEntity::class,
        ]);
    }
}

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Routing\Annotation\Route;

class MyEntityController extends AbstractController
{
    /**
     * @Route("/my-entity", name="my_entity_create", methods={"GET", "POST"})
     */
    public function create(Request $request)
    {
        $myEntity = new MyEntity();
        $form = $this->createForm(MyEntityType::class, $myEntity);
        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            // 保存实体到数据库
            // ...
        }

        return $this->render('my_entity/create.html.twig', [
            'form' => $form->createView(),
        ]);
    }
}

{{ form_start(form) }}
    {{ form_row(form.uniqueField) }}
    {{ form_errors(form) }}
    {{ form_rest(form) }}
    <button type="submit">提交</button>
{{ form_end(form) }}