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.
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.
WIP