code: private Proxy nextProxy() throws IOException {
      if (!hasNextProxy()) {
        throw new SocketException("No route to " + address.url().host()
            + "; exhausted proxy configurations: " + proxies);
      }
      Proxy result = proxies.get(nextProxyIndex++);
      resetNextInetSocketAddress(result);
      return result;
    }
docs: Returns the next proxy to try. May be PROXY.NO_PROXY but never null.