code: @Override
      String getRequestString() {
          StringBuilder requestString = new StringBuilder();
          requestString.append("fromStation=").append(fromStation).append('&');
          requestString.append("toStation=").append(toStation).append('&');
          if (viaStation != null && viaStation.trim().length() != 0) {
              requestString.append("viaStation=").append(viaStation).append('&');
          }
          if (previousAdvices != null) {
              requestString.append("previousAdvices=").append(previousAdvices).append('&');
          }
          if (nextAdvices != null) {
              requestString.append("nextAdvices=").append(nextAdvices).append('&');
          }
          if (dateTime != null) {
              requestString.append("dateTime=").append(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss").format(dateTime))
                      .append('&');
          }
          if (departure != null) {
              requestString.append("departure=").append(departure).append('&');
          }
          if (hslAllowed != null) {
              requestString.append("hslAllowed=").append(hslAllowed).append('&');
          }
          if (yearCard != null) {
              requestString.append("yearCard=").append(yearCard).append('&');
          }
          return requestString.toString();
      }
docs: {@inheritDoc}
  
  @see nl.pvanassen.ns.ApiRequest#getRequestString()