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Issue Description:

when i craft a backpack with an upgrade, i can't apply it, for all backpacks

What happens:

can't craft the backpack with the upgrade, even if it is empty

What you expected to happen:

the upgrade to be applied to the backpack
or have a description on how to apply upgrades, am i missing something?

Steps to reproduce (important):

1. place a backpack in the crafting with an upgrade, nothing happens!

...

Affected Versions (Do not use "latest"):

• IronBackpacks: IronBackpacks-1.12.2-3.0.8-12
• Minecraft: 1.12.2
• Forge: 1.12.2-14.23.4.2725
• Other Conflicting Mods (may be irrelevant to your issue):well ..

Anvil