> For those of you unwise in the ways of programming, the problem is that “null” is one of those famously “reserved” text strings in many programming languages.

It's not a text string but there are some systems that present it as such and those are the issue. Lazy programming. I remember back working for a financial institution and was told to add some validation to a service that handled adding investment plans to someone's account. The third party service we had to use was using SOAP and NULL values were represented by, you guessed it, simply putting the NULL value in the XML instead of simply omitting the item itself.

No amount of protest would make the third party service change the way it worked. "It's always worked like that and we haven't had an issue" and the "if we changed it thousands of our customers would be negatively affected! We can't do that!" were the primary excuses.