Form issue -> this works, why?

<?php

namespace Louis\DataImportBundle\Form\Type\Halcom;

use Louis\CoreBundle\Entity\Invoice\Payment;
use Louis\CoreBundle\Entity\Transaction\TransactionFee;
use Louis\DataImportBundle\Form\Type\PaymentType;
use Louis\DataImportBundle\Form\Type\TransactionFeeType;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\CollectionType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\Validator\Constraints\Valid;

class ProcessDomesticTransactionsStatementsType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        parent::buildForm($builder, $options);

        $builder
            ->add('payments', CollectionType::class, array(
                'entry_type' => PaymentType::class,
                'entry_options' => [
                    'data_class' => Payment::class,
                    'constraints' => new Valid(),
                    'validation_groups' => function(FormInterface $form) {
                        if (false === $form->get('import')->getData()) {
                            return ['__DOES_NOT_EXISTS__'];
                        }

                        return ['Default'];
                    }
                ],
                'allow_add' => false,
                'allow_delete' => false
            ))
            ->add('fees', CollectionType::class, array(
                'entry_type' => TransactionFeeType::class,
                'entry_options' => [
                    'data_class' => TransactionFee::class,
                    'constraints' => new Valid(),
                    'validation_groups' => function(FormInterface $form) {
                        if (false === $form->get('import')->getData()) {
                            return ['__DOES_NOT_EXISTS__'];
                        }

                        return ['Default'];
                    }
                ],
                'allow_add' => false,
                'allow_delete' => false
            ))
        ;
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver
            ->setDefault('novalidate', true)
            ->setDefault('validation_groups', function () {
                return ['__DOES_NOT_EXISTS__'];
            })
        ;
    }
}