code: public static Charset getCharset(CharSequence contentTypeValue) {
          if (contentTypeValue != null) {
              return getCharset(contentTypeValue, CharsetUtil.ISO_8859_1);
          } else {
              return CharsetUtil.ISO_8859_1;
          }
      }
docs: Fetch charset from Content-Type header value.
  
  @param contentTypeValue Content-Type header value to parse
  @return the charset from message's Content-Type header or {@link CharsetUtil#ISO_8859_1}
  if charset is not presented or unparsable