### Question:
BooleanUtil { public static boolean isNull(Object o) { return o == null; } private  BooleanUtil(); static boolean valueOf(String value); static boolean isNull(Object o); static boolean isNotNull(Object o);  }### Answer:
@Test public void isNullTest() { Object o = new Object(); Object n = null; Assert.assertFalse(BooleanUtil.isNull(o)); Assert.assertTrue(BooleanUtil.isNull(n)); }