code: public static File[] listExtensions(String extensionDir) {
      File[] extensions = new File(extensionDir)
          .listFiles(file -> file.getPath().toLowerCase().endsWith(Constants.EXTENSION_JAR));
      if (extensions == null) {
        // Directory does not exist
        return EMPTY_EXTENSIONS_LIST;
      }
      return extensions;
    }
docs: List extension jars from the configured extensions directory.
  
  @param extensionDir the directory containing extensions
  @return an array of files (one file per jar)