code: private static Response make(final Response res, final CharSequence type,
          final Opt<Charset> charset) {
          final Response response;
          if (charset.has()) {
              response = new RsWithHeader(
                  new RsWithoutHeader(res, RsWithType.HEADER),
                  RsWithType.HEADER,
                  String.format(
                      "%s; %s=%s",
                      type,
                      RsWithType.CHARSET,
                      charset.get().name()
                  )
              );
          } else {
              response = new RsWithHeader(
                  new RsWithoutHeader(res, RsWithType.HEADER),
                  RsWithType.HEADER,
                  type
              );
          }
          return response;
      }
docs: Factory allowing to create {@code Response} with the corresponding
  content type and character set.
  @param res Original response
  @param type Content type
  @param charset The character set to add to the content type header. If
  absent no character set will be added to the content type header
  @return Response