hi there, Just curious, why the approach of errors and if/unless logic instead of raising an exception of the class invariants are not set? i would think it'd be much simpler to use an exception for this and keep the service logic simpler and easier to test (esp for a more complex service). I remember hearing "experts" (like Sandi Metz) say this was ok to use exceptions for business logic rule errors, and this would seem to be one). Thanks!