Game crashes when cage fails to cast modded mob to ComplexMob

Steps to reproduce the behavior:
Attempting to capture a goblin from the goblin traders mod in a cage causes a game crash.

Crash Log
log

Version (please complete the following information):

• Minecraft version: 1.16.5
• Version of the mod: 1.5.3
• Additional mods: https://www.curseforge.com/minecraft/mc-mods/goblin-traders

Of course, this is the mandatory "I forgot to disable a debug thing" crash. Expect another version sometime today