Your build.gradle adds information to the built jar META-INF about an access transformer file.
However, that file does not exist.

Hence, I cannot use the universal jar of ToughAsNails as a deobf dependency to my project because gradle fails on decompilation with a Nullpointer exception triggered by the specified but missing AT.

Could you either remove the statement manifest or add an (empty) AT file? Thank You.

Off Topic:
I know there is an API artifact (which works fine), but unfortunately I need access to the Potion classes. I want to replace the hypothermia one with a version that does not affect vampires TeamLapen/VampirismIntegrations#15