Added mod to server, server crashes on load with the attached error.

https://hatebin.com/nqqlwpilbj

magicfeather-1.15.1-2.2.0.jar Magic Feather
Forge 30.0.39

Thanks for the report, I'll be pushing a fix to curseforge in a minute (testing outside of dev env first)

Here you go, file should be available in a few https://www.curseforge.com/minecraft/mc-mods/magic-feather/files/2859996