Function specified in criteria has returned null value and it cannot be evaluated

Function specified in criteria has returned null value and it cannot be evaluated

Im trying to evaluate if a variable is null. It doesnt matter if i use .isBlank() or .isNull() the line always returns: "value cannot be evaluated". I dont know how to handle this type of scenario. 

Error: Function specified in criteria has returned null value and it cannot be evaluated Line:(5)

I run this script on User Input

  1. if(input.Action_Quote == "Edit")
  2. {
  3. input.Action_Quote = null;
  4. currentRecord = Quotes[ID == input.ID];
  5. if( currentRecord.isBlank())
  6. {
  7. info "work";
  8. }
  9. else 
  10. {
  11. info "it doesnt";
  12. }