code: protected function makePassengerIfNeeded()
      {
          if (count($this->passengerData[0]->travellerInformation->passenger) < 1) {
              $this->passengerData[0]->travellerInformation->passenger[0] = new Passenger(null, null);
          }
      }
docs: If there is no passenger node at
  $travellerInfo->passengerData[0]->travellerInformation->passenger[0]
  create one