Adding a Compendium Weapon to a Creature or NPC sheet when using a custom Skill list prevents sheet rendering

[Re4XN]

Describe the bug
If a world is using a custom list of Skills, adding the default Weapon Items to a Creature or NPC sheet will result in erroneous data preparation if the associated Skill doesn't exist. After the sheet is closed, any further attempts to open it result in an error.

To Reproduce
Steps to reproduce the behavior:

1. Create new Skill list
2. Set new Skill list as default
3. Create new NPC Actor
4. Right click '+Add' on the Attack Profiles
5. Drag a Weapon onto the sheet
6. Close the sheet
7. Attempt to open the sheet again

Expected behavior
The weapon should be added (even with the incorrect skill) and the GM should be able to open the sheet.

Additional context
See:

• creature-sheet.js line 137.