code: /** 
   * Verify progress callback doesn't cause an exception when it's null
   * @throws Exception
   */
  @Test public void nullUploadProgress() throws Exception {
    final AtomicReference<String> body=new AtomicReference<String>();
    handler=new RequestHandler(){
      @Override public void handle(    Request request,    HttpServletResponse response){
        body.set(new String(read()));
        response.setStatus(HTTP_OK);
      }
    }
  ;
    File file=File.createTempFile("post",".txt");
    new FileWriter(file).append("hello").close();
    int code=post(url).progress(null).send(file).code();
    assertEquals(HTTP_OK,code);
    assertEquals("hello",body.get());
  }
  