added raise_error in TypeVariable.deref for unresolved type vars.
added raise_error in TypeVariable.deref for unresolved type vars.

iamrekcah/clay,aep/clay,jckarter/clay,mario-campos/clay,mario-campos/clay,jckarter/clay,mario-campos/clay,aep/clay,mario-campos/clay,aep/clay,jckarter/clay,aep/clay,aep/clay,iamrekcah/clay,iamrekcah/clay,mario-campos/clay,jckarter/clay,iamrekcah/clay,iamrekcah/clay,aep/clay,jckarter/clay,jckarter/clay