### Question:
ListMemoizer { public M get(final ListNode<T> list) { if (null == list) { throw new IllegalArgumentException("null key"); } return (null == helper) ? null : helper.get(list); } ListMemoizer(final Comparator<T> comparator); M get(final ListNode<T> list); boolean put(final ListNode<T> list, final M memo); boolean remove(final ListNode<T> list);  }### Answer:
@Test public void testEmptyMemoizer() throws Exception { ListMemoizer<String, Integer> m = createMemoizer(); assertNull(m.get(createList())); assertNull(m.get(createList("foo"))); assertNull(m.get(createList("foo", "bar"))); }