code: public void activateOptions() {
        // find out period from the filename pattern
        if (fileNamePatternStr != null) {
          parseFileNamePattern();
        } else {
          LogLog.warn(FNP_NOT_SET);
          LogLog.warn(SEE_FNP_NOT_SET);
          throw new IllegalStateException(FNP_NOT_SET + SEE_FNP_NOT_SET);
        }
  
    }
docs: {@inheritDoc}