code: public static Parameter<String> decodeForm(String s, Charset charset) {
          int idx = s.indexOf("=");
          try {
              if (idx < 0) {
                  return Parameter.of("", URLDecoder.decode(s, charset.name()));
              }
              return Parameter.of(URLDecoder.decode(s.substring(0, idx), charset.name()),
                      URLDecoder.decode(s.substring(idx + 1), charset.name()));
          } catch (UnsupportedEncodingException e) {
              // should not happen
              throw new RequestsException(e);
          }
      }
docs: Decode key-value query parameter