code: private String getFeatureString(Set<String> featureNames) {
          StringBuilder featureBuilder = new StringBuilder();
  
          if (featureNames != null) {
              Iterator<String> iter = featureNames.iterator();
              while (iter.hasNext()) {
                  featureBuilder.append(iter.next());
                  if (iter.hasNext())
                      featureBuilder.append(',');
              }
          }
          return featureBuilder.toString();
      }
docs: Build a comma separated string based on the set of feature names.
  
  @return