hardcoding the refmap and not generating it will cause mixin to warn users that it is missing. either remove the hardcoded reference or generate the refmap as part of your build process.

[main/WARN] [mixin/]: Reference map 'arts_and_crafts.refmap.json' for arts_and_crafts-common.mixins.json could not be read. If this is a development environment you can ignore this message