Describe the bug

on the master branch, crafting patterns with empty slots are invalid.
presumably, this happens because air is encoded and interpreted as part of the recipe. (see screenshot)

How to reproduce the bug

create a valid crafting pattern where at least one slot is empty and encode it

Expected behavior

The pattern to be valid

Additional details

Which minecraft version are you using?

1.17

On which mod loaders does it happen?

Fabric

Crash log

https://gist.github.com/Mari023/acc2ebad606901c14d9fd3b1601e4b67

Fixed in #5681.