[recursive]

I don't know lua. But the behavior you describe seems like a quirk of lua tables. Instead of having `table.get(key)` return a sentinel value, you can replace it with `table.has_key(key)` and `table.get(key)`.

I'm not sure about the ergonomics of the trade in lua. But in C# the ergonomics of `DBNull` are terrible. If it were just replaced with `null` everywhere, everything would just be better.

IMHO.