code: public Sender getResponseSender() {
          if (blockingHttpExchange != null) {
              return blockingHttpExchange.getSender();
          }
          if (sender != null) {
              return sender;
          }
          return sender = new AsyncSenderImpl(this);
      }
docs: Get the response sender.
  <p>
  For blocking exchanges this will return a sender that uses the underlying output stream.
  
  @return the response sender, or {@code null} if another party already acquired the channel or the sender
  @see #getResponseChannel()