I'm not sure this is the right logic.  If I set my profile to `james` and it's not in the shared config, we shouldn't fall back to default.  Default's only used if either they explicitly set the profile name to `default` or if they don't set any profile name at all.

Also, I'd expect that if I refer to a profile that does not exist, we'd eventually propagate an error back to the user rather than falling back to the `default` profile.