• This issue is not solved in a development build

Describe the bug
I get this error with latest dev build #661.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'NPC'
2. Click on 'any menu option'
3. Scroll down to '....'
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
If applicable, add screenshots to help explain your problem.

Version Info
Provide your ProtocolLib install info with /protocol dump through pastebin.

Additional context
Add any other context about the problem here.
Nothing that I can understand

Update the IllegalStack plugin to the latest version: https://www.spigotmc.org/resources/dupe-fixes-illegal-stack-remover.44411/update?update=508650