I have a Custom product which when added to cart, I intend to validate the cart and ensure the custom product meets certain criterias before checkout.
Please see Shopware Documentation: Add Cart Validator.

class CustomCartValidator implements CartValidatorInterface
{
    public function validate(Cart $cart, ErrorCollection $errorCollection, SalesChannelContext $salesChannelContext): void
    {
        foreach ($cart->getLineItems()->getFlat() as $lineItem) {
          if($lineItem->getQuantityInformation() === null){
            continue;
          }
          
          //use the quantity information here

        }
    }
}

The $lineItem->getQuantityInformation() always returns NULL. But if I var_dump($lineItem->getQuantityInformation()), it outputs the correct information.

How do I solve this problem?