@Test
public void testSingletonMap_nullkey() {

  Map<String, String> map = new HashMap<>();
  map.put(null, "BAD");
  try {
    @SuppressWarnings("unused")
    SegmentTrie<String> unused = SegmentTrie.create(map, '.', DEFAULT);
    fail("expected NullPointerException");
  } catch (NullPointerException e) {
    // pass
  }
}