code: public static Path addExtension(Path path, String... extensions) {
      StringBuilder pathStringBuilder = new StringBuilder(path.toString());
      for (String extension : extensions) {
        if (!Strings.isNullOrEmpty(extension)) {
          pathStringBuilder.append(extension);
        }
      }
      return new Path(pathStringBuilder.toString());
    }
docs: Suffix all <code>extensions</code> to <code>path</code>.
  
  <pre>
  PathUtils.addExtension("/tmp/data/file", ".txt")                          = file.txt
  PathUtils.addExtension("/tmp/data/file.txt.gpg", ".zip")                  = file.txt.gpg.zip
  PathUtils.addExtension("/tmp/data/file.txt", ".tar", ".gz")               = file.txt.tar.gz
  PathUtils.addExtension("/tmp/data/file.txt.gpg", ".tar.txt")              = file.txt.gpg.tar.txt
  </pre>
  
  @param path to which the <code>extensions</code> need to be added
  @param extensions to be added
  
  @return a new {@link Path} with <code>extensions</code>