code: protected RequestConfig createConfig() {
      if (proxy == null && socketTimeout < 0 && connectTimeout < 0) {
        return null;
      }
      Builder builder = RequestConfig.custom();
      if (proxy != null) {
        builder.setProxy(proxy);
      }
      if (socketTimeout >= 0) {
        builder.setSocketTimeout(socketTimeout);
      }
      if (connectTimeout >= 0) {
        builder.setConnectTimeout(connectTimeout);
      }
      return builder.build();
    }
docs: 创建配置
  
  @return 如果没有自定义配置，返回值为null