code: private static String getFileExtension(String path) {
          int index = path.lastIndexOf('.');
          if (index == -1) {
              return null;
          }
  
          return path.substring(index + 1).toLowerCase(Locale.ENGLISH);
      }
docs: returns lower cased extension
  
  TODO: if we support the path being a folder (to be zipped), then
  this method will need to be smarter in terms of searching for an "extension"