表单查询symfony 3.4中的空选项

use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
use Symfony\Component\Form\Extension\Core\Type\SubmitType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;

class MyFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            // 其他字段...
            ->add('myField', ChoiceType::class, [
                'choices' => [
                    '空选项' => null, // 设置空选项
                    '选项1' => 'value1',
                    '选项2' => 'value2',
                    // 其他选项...
                ],
                'placeholder' => '请选择', // 设置空选项的标签
                'required' => false, // 设置字段为可选
            ])
            ->add('submit', SubmitType::class, ['label' => '提交'])
        ;
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            // 表单配置项...
        ]);
    }
}