->addEventListener(FormEvents::POST_SUBMIT, function (FormEvent $event) {
                /** @var \Eccube\Entity\Shipping $data */
                $data = $event->getData();
                /** @var \Symfony\Component\Form\Form $form */
                $form = $event->getForm();
                $shippingDeliveryDate = $form['shippingDeliveryDate']->getData();
                if (!empty($shippingDeliveryDate)) {
                    $data->setShippingDeliveryDate(new \DateTime($form['shippingDeliveryDate']->getData()));
                } else {
                    // 画面下部にエラーメッセージを表示させる
                    $form['shippingDeliveryDate']->addError(new FormError('お届け日は必ず指定してください。'));
//                    $data->setShippingDeliveryDate(null);
                }
            });

                                <label>お届け日</label>
                                {{ form_widget(form.shippings[idx].shippingDeliveryDate) }}<br class="sp">

                                <label>お届け日</label>
                                {{ form_widget(form.shippings[idx].shippingDeliveryDate) }}{{ form_errors(form.shippings[idx].shippingDeliveryDate) }}<br class="sp">