code: private static void encodeFormFields(final StringBuilder sb, final String content, final Charset charset) {
          urlEncode(sb, content, (charset != null) ? charset : Charsets.UTF_8, URLENCODER, true);
      }
docs: Encode/escape www-url-form-encoded content.
  <p>
  Uses the {@link #URLENCODER} set of characters, rather than the {@link #UNRSERVED} set; this is for compatibilty
  with previous releases, URLEncoder.encode() and most browsers.
  @param content
  the content to encode, will convert space to '+'
  @param charset
  the charset to use
  
  @return encoded string