It might be confusing, but it does seem correct. It’s not an error if a channel has no community set, so it should be a 2xx code. I would understand a 404 as “that channel doesn’t exist”, although currently that seems to be 400. I think it’s more important to actually document all the possible response codes for all endpoints.
If it does get changed it should be communicated/documented as well, otherwise it could lead to problems when clients suddenly receive an error instead of an “All good, just nothing here” response (or just a changed/unexpected response in general).