Sylius\Bundle\PromotionBundle\Form\Type\PromotionCouponToCodeType::transform PHP Method

    public function transform($coupon)
    {
        if (null === $coupon) {
            return '';
        }
        if (!$coupon instanceof PromotionCouponInterface) {
            throw new UnexpectedTypeException($coupon, PromotionCouponInterface::class);
        }
        return $coupon->getCode();
    }