public static boolean equals(CharSequence s1, CharSequence s2) {
        return s1 == null ? s2 == null : s1.equals(s2);
    }
@Test
    public void testEquals() {
        Assert.assertTrue(StringUtils.equals(null, null));
        Assert.assertFalse(StringUtils.equals(null, ""));
        Assert.assertFalse(StringUtils.equals("", null));
        Assert.assertTrue(StringUtils.equals("", ""));
        Assert.assertFalse(StringUtils.equals("1", "2"));
        Assert.assertTrue(StringUtils.equals("1", "1"));
    }