code: private String readExtensions(final String featureName) {
          final Set<String> exts = new HashSet<>();
          if (featureTable.containsKey(featureName)) {
              for (final Value ext : featureTable.get(featureName)) {
                  final String e = ext.value.trim();
                  if (e.length() != 0) {
                      exts.add(e);
                  }
              }
          }
          return StringUtils.join(exts, CONF_LIST_SEPARATOR);
      }
docs: Read plug-in feature.
  
  @param featureName plug-in feature name
  @return combined list of values