Exception in server tick loop
java.lang.NullPointerException

Description: I've been running around in singleplayer, jumped into a river and my game froze giving me this crashreport.
https://pastes.dev/5IarQAPXT3

Minecraft 1.12.2
Forge 14.23.5.2859
198 Mods
World: Singleplayer
Modversion: UndergroundBiomesConstructs-1.12-1.3.13
Optifine: Yes
Reproducing: I've tried to reproduce the problem but it seems to happen at random.

weirdly i just got the same error.

How many mods were you using?
i was just updating some mods in my pack and then that happened, very odd.

It's the worldgen bug with slab replacement. Previous fix was misplaced.