Fixes #20 - Transformations should work on groups with no values

- Updated Base and ResultSet to handle empty values in groups
- Added a test
Full-elf = Elf; clearly someone is not versed in the world of fantasy
I enjoy pry but I keep forgetting to remove it before I commit, I suck.
Merge pull request #21 from liftopia/issue_20

Fixes #20 - Groups with no values will not longer break transformations