Symfony 2.8 - Enforce minimum select amount for the form with integer data form fields

ProductsFormType.php

// ...

$builder->addEventListener(FormEvents::SUBMIT, function(FormEvent $event) {
    $form = $event->getForm();

    $productsAmount = array_reduce($form->all(), function($carry, $item) {
        $carry += (int) $item->getData();
        return $carry;
    }, 0);

    if ($productsAmount < 1) {
        $form->addError(new FormError('Please select products'));
    }
});

// ...