Don't know if it's a stock bug, data.prototype screwing up or some other mod doing stupid things, but to get your mod to work I had to manually coerce items.stack_size to an int, it seems to be a string in the latest build for some reason.

Lines 6 of data-updates.lua needs to be:
if items.stack_size and tonumber(items.stack_size) > 1 then

Good afternoon!
Maybe a new version of the game has come out and something has changed, unfortunately I still could not handle the mod. If the error really turns out to be relevant, I'll try to fix it.
I also want to change something - to make it as bob's mod and etc., to configure the mod could be in the game in the settings, and not by editing the config in the archive, but I do not know how to do it, but there are guesses.