Forge version: 2738
Optifine: U-D1
Minecraft version: 1.12.2
Random Things Version: 4.1.9

Crash Log: https://hastebin.com/awaqabonuh.coffeescript

What happens? Either when holding, placing, or picking up entities, the client crashes.

Just happened again, it's when left clicking the summoning pendulum from the inventory screen, with at least one entity inside, while the item is in the hotbar.

Not 100% sure whether this fixes this because i can't reproduce it but it should.