Crashed when trying to create a prefab variant.

Steps to reproduce
- Open linked project https://tinyurl.com/y8wode5j (BiscuitOlympics).
- Open the Character Creation Scene.
- Select the Rich Tea character in the hierarcy.
- Drag and drop it into the Character Prefabs folder in the project menu.
- Unity prompts the user if they would like a new prefab or a variant.
- Select Variant.
NOTICE ISSUE - Crash.

VIDEO ATTACHED
PROJECT: https://tinyurl.com/y8wode5j