assertFalse(attribute.containsKey(null));
assertFalse(attribute.containsValue(null));
attribute.put(null, null);
attribute.put(null, null);
assertEquals(1, attribute.size());
assertTrue(attribute.containsKey(null));
assertTrue(attribute.containsValue(null));
assertNull(attribute.get(null));
String value = "It's null";
attribute.put(null, value);