https://pastebin.com/PMMVkTPV

I was pregenerating chunks when I got this crash.

Based on what I see on the line of code where it breaks this seems to be a case of unregistered biome. What mod do you use for world gen?

This crash also happens in the nether.

Quark's realistic setting. The only other biome mod is Traverse.

I have released a new version of aw the day before yesterday that should hopefully fix the issue. Let me know if that helped and if you see anything new in logs - I have added logging of unregistered biomes in there.

Have you seen this happening since the last release? if not I will close.

No, so far so good; will update if it comes up again though. It was very, very infrequent, I believe 3 instances over 2.6M chunks pregenerated.