Symfony 4 CollectionType验证组不工作

use Symfony\Component\Form\Extension\Core\Type\CollectionType;
use Symfony\Component\Validator\Constraints\NotBlank;

// ...

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('collectionField', CollectionType::class, [
            'entry_options' => [
                'constraints' => [
                    new NotBlank(),
                    // other validation constraints
                ],
            ],
        ]);
}

use Symfony\Component\HttpFoundation\Request;

// ...

public function submitForm(Request $request)
{
    $form = $this->createForm(MyFormType::class);
    $form->handleRequest($request);

    if ($form->isSubmitted() && $form->isValid()) {
        // process form data
    }

    // render form template
}