如何在自定义symfony表单字段类型中默认为empty_value选项？

namespace App\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
use Symfony\Component\OptionsResolver\OptionsResolver;

class CustomChoiceType extends AbstractType
{
    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'choices' => [
                'Option 1' => 'option_1',
                'Option 2' => 'option_2',
                'Option 3' => 'option_3',
            ],
            'empty_value' => '请选择一个选项',
        ]);
    }

    public function getParent()
    {
        return ChoiceType::class;
    }
}

namespace App\Form;

use App\Form\Type\CustomChoiceType;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;

class CustomFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('custom_field', CustomChoiceType::class);
    }
}