docs: private void addStopwords(String dir) {
  		if (dir == null) {
  			logger.info("no stopwords dir");
  			return;
  		}
  		logger.info("stopwords: {}", dir);
  		filter = new HashSet<String>();
  		File file = new File(dir);
  		try (FileInputStream fis = new FileInputStream(file)) {
  			InputStreamReader reader = new InputStreamReader(fis, "UTF-8");
  			BufferedReader br = new BufferedReader(reader);
  			String word = br.readLine();
  			while (word != null) {
  				filter.add(word);
  				word = br.readLine();
  			}
  		} catch (FileNotFoundException e) {
  			logger.info("No stopword file found");
  		} catch (IOException e) {
  			logger.info("stopword file io exception");
  		}
  	}