Collections.reverse(list);
Iterator it = list.iterator();
Object confirmedLast = it.next();
while (it.hasNext()) {
Object confirmedObject = it.next();
assertEquals(confirmedObject, bidi.previousKey(confirmedLast));
confirmedLast = confirmedObject;
}
assertEquals(null, bidi.previousKey(confirmedLast));
if (isAllowNullKey() == false) {