Describe the Bug:
The mod always crashes when clicking the "done" button on any in-game config sub-menu and saves no setting.

How to Reproduce:

1. Launch the game
2. Click "Mods" on the main menu > "Infernal Expansion" > "Config" > E.g. "Mob Interactions..." (any sub-menu) > "Done"
3. "Saving World" is shown for a short while
4. The game crashes

Expected Behavior:
The crash shouldn't be caused and the mod should save settings.
Additional info: The mod won't generate any file in my config and config\infernalexp folders except for the config\infernalexp\spawnrates folder, which contains nine [mob name].json files. Is that normal?

Error message (Minecraft launcher):

The game crashed whilst mouseclicked event handler
Error: java.lang.NullPointerException: Cannot set config value without assigned Config object present
Exit code: -1

Version Information:

• Operating System: Windows 7
• Mod Version: 2.3.1
• Minecraft Version: 1.16.5 (tried on both default folder and new custom folder)
• Forge Version: tried both 36.2.6 and 36.2.0
• Other mods that were running when the crash happened: No other mods. Tried only with Infernal Expansion

Additional Context:
A crash report here
crash-2021-10-11_11.55.05-client.txt

It's fixed by 2.3.2. Thank you