[2.1] Fixed A Major Issue With The Groups

I did some debugging that uncovered that the `getGroup` function was not behaving as we expected. It was not returning `null` when there was no group prefix, but was in fact returning the model class name. I've fixed this, and also corrected a typo in the `getModelClass` function that we were actually getting away with before due to the broken `getGroup` function.

---
//cc @scottrobertson