code: public URLNormalizer removeDirectoryIndex() {
          String path = toURL().getPath();
          if (PATTERN_PATH_LAST_SEGMENT.matcher(path).matches()) {
              url = StringUtils.replaceOnce(
                      url, path, StringUtils.substringBeforeLast(path, "/") + "/");
          }
          return this;
      }
docs: <p>Removes directory index files.  They are often not needed in URLs.</p>
  <code>http://www.example.com/a/index.html &rarr;
  http://www.example.com/a/</code>
  <p>Index files must be the last URL path segment to be considered.
  The following are considered index files:</p>
  <ul>
  <li>index.html</li>
  <li>index.htm</li>
  <li>index.shtml</li>
  <li>index.php</li>
  <li>default.html</li>
  <li>default.htm</li>
  <li>home.html</li>
  <li>home.htm</li>
  <li>index.php5</li>
  <li>index.php4</li>
  <li>index.php3</li>
  <li>index.cgi</li>
  <li>placeholder.html</li>
  <li>default.asp</li>
  </ul>
  <p><b>Please Note:</b> There are no guarantees a URL without its
  index files will be semantically equivalent, or even be valid.</p>
  @return this instance