Known, I believe this was fixed once already but maybe never got applied/regressed with msgpack refactors, issue is internally Lua tables are used and as known Lua tables can’t contain nil.
A fix was never applied and should still be residing on one of my abandoned branches. Although, it can be improved since: msgpack.null() == msgpack.null and stored as an upval in scheduler.lua.
I don’t have the ability to test the fix on client at the moment so I cannot guarantee it causing any regressions.