Basically, ignore any advice to treat Nil as a normal value, because it really is intended to represent the *absence* of a value as much as possible. It's a bit like the way solid-state electronics treats "holes" as if they were real particles, and gets away with it much of the time. But not all the time, because the hole isn't real; it's the collective behavior of everything around a thing that's missing.
So while you can test explicitly for Nil if you try hard enough, it's better not to try at all, because lots of places internally are using that Nil to select some kind of default behavior that might or might not look like Nil afterwards. It was probably a mistake to put Nil into the type hierarchy underneath the Any type in the first place. It's more of a concept type like Junction, so probably belongs outside of Any, which sits the top of the "normal" object hierarchy. These types are deeply magical. Whenever you find yourself trying to use Nil or Junction as a normal value, you have to ask yourself whether you're just Mickey Mouse falling into the Sorcerer's Apprentice trap. Unless you're a wizard, with Nil and Junction it's better to cargo cult a few common usages and stay the heck away the rest of the time. Larry
