Problem/Motivation
It is now necessary that a module is enabled, so that the service exists to use it.
I don't think that is bad but I think we could handle the fact that the service doesn't exist much more nicely and simply fall back to the default if not provided.
Proposed resolution
In CacheFactory::get(), check if the specified service in $cache_settings exists before calling it (bin specific and default). Don't check the default backends. Should be possible to simply specify that inline in the existing if cases.