Versions

• Curios: curios-forge-5.4.2+1.20.1.jar
• Forge: 47.2.6

Observed Behavior:

Error

Expected Behavior:

No Error

Steps to Reproduce:

1. Enable Curios API
2. Enable Iron's Spells and Spellbooks
3. Crash.

Crash Log:
https://pastebin.com/sHtN28ZP

The crash does not occure with the mod "Tiered" is disabled
Issue created over at "Tiered" page Stereowalker/Reforged#65

This is an issue coming from Tiered, there's nothing I can do from my end.