If I'm understanding this correctly, it's still a problem: if the product's price element or the order's line item list is null, for example, that shouldn't just be silently ignored. The transaction should fail, loudly and visibly (like with an exception) so that the root cause of the invalid data can be examined. The way most programmers code it is to just ignore the bad data and potentially ship an item for free, or without charging tax, or charge the customer but not ship the item, etc. etc. This is why so many software development organizations have huge QA departments.