code: public function isValid()
      {
          if (AddressValidation::REQUEST_OPTION_ADDRESS_CLASSIFICATION == $this->requestAction) {
              return $this->response->AddressClassification->Code > 0;
          }
          return isset($this->response->ValidAddressIndicator);
      }
docs: Tells whether or not the ValidAddressIndicator is present on the XML document.
  This indicator is present if provided address is valid and represents a
  single, unique address in the UPS Address Validation system.
  
  @return bool