code: public URLNormalizer addDirectoryTrailingSlash() {
          String urlRoot = HttpURL.getRoot(url);
          String path = toURL().getPath();
          String urlRootAndPath = urlRoot + path;
  
          String name = StringUtils.substringAfterLast(path, "/");
          if (StringUtils.isNotBlank(name) && !name.contains(".")) {
              String newPath = path + "/";
              String newUrlRootAndPath = urlRoot + newPath;
              url = StringUtils.replaceOnce(
                      url, urlRootAndPath, newUrlRootAndPath);
          }
          return this;
      }
docs: <p>Adds a trailing slash (/) to a URL ending with a directory.  A URL is
  considered to end with a directory if the last path segment,
  before fragment (#) or query string (?), does not contain a dot,
  typically representing an extension.</p>
  
  <p><b>Please Note:</b> URLs do not always denote a directory structure
  and many URLs can qualify to this method without truly representing a
  directory. Adding a trailing slash to these URLs could potentially break
  its semantic equivalence.</p>
  <code>http://www.example.com/alice &rarr;
  http://www.example.com/alice/</code>
  @return this instance
  @since 1.11.0 (renamed from "addTrailingSlash")