code: @Test public void test_addParameterIfAbsent() throws Exception {
    URL url=URL.valueOf("dubbo://admin:hello1234@10.20.130.230:20880/context/path?application=morgan");
    url=url.addParameterIfAbsent("application","xxx");
    assertEquals("dubbo",url.getProtocol());
    assertEquals("admin",url.getUsername());
    assertEquals("hello1234",url.getPassword());
    assertEquals("10.20.130.230",url.getHost());
    assertEquals(20880,url.getPort());
    assertEquals("context/path",url.getPath());
    assertEquals(1,url.getParameters().size());
    assertEquals("morgan",url.getParameter("application"));
  }
  