On the contrary, apparently you're unaware that a ton of languages and serialization formats have ‘null’. And there's nothing special about nil in Lua, it's just called ‘undefined’ in other dynamic languages (possibly with minor differences). Lua doesn't have a proper ‘null’.

But yeah, this discussion is pointless since you're obviously not concerned either about the use-cases of exchanging data with languages that are not like C, or about keeping structures ‘schemaless’ in Lua code.