code: public MultipartBuilder addFormDataPart(String name, String value) {
          return addFormDataPart(name, null, new NetworkRequest.Builder()
                  .setContentType((MediaType)null)
                  .setBody(value.getBytes(Charset.forName(HTTP.DEFAULT_CONTENT_CHARSET)))
          .build());
      }
docs: Add a form data part to the body.