Fix validation to skip performing a query if the field is blank
Merge pull request #10 from MountainRoseHerbs/2-3-stable-mrh-fix-unecessary-uniqueness-query

Remove unnecessary uniqueness query
Add validation for the presence of adjustable

* Adjustments without an adjustable item do not make too much sense
* Enforcing an adjustable is always present will make it easier to find
  bugs in related code.