In my previous job my main responsibility was supporting a VFP app that had been written by a FoxPro DOS guy. More like a dBASE III guy. He neither understood nor used most VFP features. One area where we had particular problems was with nulls. My boss estimated 80% of our customer service calls turned out to be caused by nulls. I wrote a couple of simple utility programs that churned through tables or the entire DBC looking for nulls and fixing them. We put it into the application and instructed the first line client care staff to have clients run those programs and then call us back. In many cases they didn't have to call back.

Like many things, support for nulls is a dangerous tool in careless hands.