@Test
public void getGravatarUrlTest() {

    Assert.assertEquals("https://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61.jpg?d=mm", GravatarUtil.getGravatarUrl("admin@example.com"));
    String s = null;
    Assert.assertEquals("https://www.gravatar.com/avatar/00000000000000000000000000000000.jpg?d=mm", GravatarUtil.getGravatarUrl(s));
}