An empty mod does not contain any car / helmet / pitcrew / tyre / gpaedia / etc updates. It is just a set of empty folders and settings files created for you to fill in with your own updates. It means you don't need to know exactly how everything in a CSM mod works; you just download updates and put them in the correct folders, and it will just work.
It is for people who prefer to create their own mods but don't want to spend lots of time messing around with CSM settings files.
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Intel NUC 8i3, 8GB RAM, MS Sidewinder Wheel