Follow up to MC-236224: This issue is replicated in a vanilla minecraft environment, using the vanilla launcher and an unmodified game JAR (no Optifine or mod loaders).
I am getting fatal NPEs thrown by Minecraft in chunk generation when using world generation datapacks. I have had them thrown while doing initial spawn area generation on creating a new world, and on exploring a world.
I have seen similar issues (NPEs ending in "because "☃" is null" or "because "☃" is null") in the bug tracker get fixed, but I haven't seen one for cyc.a(java.util.Random) yet.
I attached my log file from my vanilla replication, and my list of data packs. My world save is too big to attach, I've put it up at Dropbox (recreated from scratch w/out optifine) - this of course includes all the datapacks.
Please check if this is still an issue in 1.18.1.