Hello all,
1.15.9 has been reported to have a serious bug. I failed to test if the mod still worked without angels installed (which is what I assume most people play) and missed the glaring mistake that if an array does not exist the game throws an error even if it is supposed to check if the array existing.
This has been fixed in 1.15.10 and the game will start as normal with or without angels installed.
Sorry for the inconvenience and if you find any more bugs, I'll fix them as soon as I can.

P.S. As nagapito noted, the migration should be in a migration file. it is so now. (I adapted(stole) the original script from GDIW because I was still learning (and still am))

I encountered the error as initially described. However, I was playing with Angels and Bobs, and some other mods. Generating a new save file had no issues.
I hope there was only 1 error, and you fixed it, but perhaps there's something else lingering around and this might just point your attention to it :)
Also, perhaps you might want to keep a changelog. I was missing that on the first page so had to check the discussions to see if you fixed the error. Thanks :)

Thanks for the quick reaction!