code: @Override
      String getRequestString() {
          StringBuilder requestString = new StringBuilder();
          if (station != null && station.trim().length() != 0) {
              requestString.append("station=").append(station).append('&');
          }
          if (actual != null) {
              requestString.append("actual=").append(actual).append('&');
          }
          if (unplanned != null) {
              requestString.append("unplanned=").append(unplanned).append('&');
          }
          return requestString.toString();
      }
docs: {@inheritDoc}
  
  @see nl.pvanassen.ns.ApiRequest#getRequestString()