code: private boolean responseIsInValid() {
          if (response == null) {
              return true;
          }
          else if (!response.isHeadless() && validityCheck) {
              return request.getTransactionID() != response.getTransactionID();
          }
          else {
              return false;
          }
      }
docs: Returns true if the response is not valid
  This can be if the response is null or the transaction ID of the request
  doesn't match the reponse
  
  @return True if invalid