"Any key with value nil is not considered part of the table.
Conversely, any key that is not part of a table has an associated value nil." http://www.lua.org/manual/5.2/manual.html#2.1
I see. I did spot that but I assumed it implicitly meant "any _valid_ key that is not part of the table", etc. and I was under the impression that it was not valid (and hence an error) to index a table with nil in the first place. Funny I never tried it until now.
