->add('template', MailTemplateType::class, [
    'required' => false,
    'mapped' => false,
    'query_builder' => function (EntityRepository $er) {
        return $er->createQueryBuilder('mt')
                    ->andWhere('mt.id = :id')
                    ->setParameter('id', $this->eccubeConfig['eccube_order_mail_template_id'])
                    ->orderBy('mt.id', 'ASC');
    },
])