Dynamic/Types/CountryType.php
public function build(FormBuilderInterface $builder, FormField $field, $locale, $options = [])
    {
        if (isset($options['attr']['placeholder'])) {
            $options['placeholder'] = $options['attr']['placeholder'];
            unset($options['attr']['placeholder']);
        }

        $type = TypeCountryType::class;
        $builder->add($field->getKey(), $type, $options);
    }
public function build(FormBuilderInterface $builder, FormField $field, $locale, $options = [])
    {
        if (isset($options['attr']['placeholder'])) {
            $options['placeholder'] = $options['attr']['placeholder'];
            unset($options['attr']['placeholder']);
        }

        $type = TypeCountryType::class;
        $builder->add($field->getKey(), $type, $options);
    }
{@inheritdoc}