code: private String getWthInsiCodeOr(Map wthData) {
          String insiName = getWthInsiCode(wthData);
          if (insiName.equals("")) {
              return getNextDefName();
          } else {
              return insiName;
          }
      }
docs: Get the 4-bit institute code for weather file name, if not available from
  data holder, then use default code
  
  @param wthData Weather data holder
  @return 4-bit institute code