The null reference is so ubiquitous, such an integral part of our experience as programmers, that it would be hard to imagine a world without it. Yet it is the source of so much frustration and actual financial loss that it is well worth the effort to think about some alternatives. But what exactly is the problem? Let’s imagine we have a system where customers can place orders. The orders contain line items that have a reference to a product and they store the quantity ordered....