code: public void addParam(String name, String value) {
          ObjectUtil.checkNotNull(name, "name");
          if (hasParams) {
              uriBuilder.append('&');
          } else {
              uriBuilder.append('?');
              hasParams = true;
          }
          appendComponent(name, charsetName, uriBuilder);
          if (value != null) {
              uriBuilder.append('=');
              appendComponent(value, charsetName, uriBuilder);
          }
      }
docs: Adds a parameter with the specified name and value to this encoder.