code: public ProxyService build() {
          return new ProxyServiceImpl(getReactor(), getTimer(), getHttpClientBuilder(), getBeforeSend(),
                  getErrorHandler(), getHttpClientRequestPredicate(), getCheckClientDuration(),
                  pingBuilder == null ? Optional.<HttpRequestBuilder>empty() : Optional.of(pingBuilder),
                  isTrackTimeOuts(), getTimeOutInterval());
      }
docs: Build the impl.
  
  @return returns an instance of the impl.