Describe the bug
A clear and concise description of what the bug is.
Info on what other mods you're using that may cause a conflict here if applicable.
When doing the steps below your client and the server will both crash

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To Reproduce
Steps to reproduce the behavior:
It’s when you put something that isn’t an upgrade into an upgrade slot

It crashes your game and the server apparently
Expected behavior
A clear and concise description of what you expected to happen.
Server and client instantly crashes

Screenshots
If applicable, add screenshots to help explain your problem.
The server keeps crashin

Versions
Mod version that you're using. Version of forge may also be helpful in some cases
Sophisticatedbackpacks-1.6.4-2.2.8.232.jar

Error Log
crash-2021-04-07_00.15.23-server.txt

This is fixed in version 234 - second to last as of now. In that version it again properly checks for only upgrades going into the slot in all scenarios. However if you already have a backpack with another item in upgrade slot that won't stop this crash. you will need to ditch the backpack / load from backup or edit the nbt of the backpack to get the item out of there.