v1.0 error in my mod

[BaconHer0]

Hey guys, I'm getting a 1 time error message pop-up when right clicking on either core or custom apparel in my mod. Does anyone know where the error comes from?

It doesn't affect gameplay and the pop-up doesn't come back up again, so it's not a major issue but it's something I'd like to fix.
This error did not appear in B19

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