As for now, two tasks to solve:
1) Find 41-byte solution compatible with Lua 5.1, 5.2 and 5.3
2) Find 36-byte solution for latest version of Lua
NVL=load"return({...})[#...+2]or..."
OK, 36-byte solution for latest Lua version has been found (exactly as mine one)!
Only one task is remaining to solve. Try to find 41-byte solution for Lua 5.1 My solution for the remaining task is based on some Lua feature which looks like a design bug for me.