public HollowOrdinalIterator findKeysWithPrefix(String prefix) {
        TST current;
        HollowOrdinalIterator it;
        do {
            current = prefixIndexVolatile;
            it = current.findKeysWithPrefix(prefix);
        } while (current != this.prefixIndexVolatile);
        return it;
    }
@Test
    public void testMovieMapReference() throws Exception {
        Map<Integer, String> idActorMap = new HashMap<>();
        idActorMap.put(1, "Keanu Reeves");
        idActorMap.put(2, "Laurence Fishburne");
        idActorMap.put(3, "Carrie-Anne Moss");
        MovieMapReference movieMapReference = new MovieMapReference(1, 1999, "The Matrix", idActorMap);
        objectMapper.add(movieMapReference);
        StateEngineRoundTripper.roundTripSnapshot(writeStateEngine, readStateEngine);
        HollowPrefixIndex prefixIndex = new HollowPrefixIndex(readStateEngine, "MovieMapReference", "idActorNameMap.value");
        Set<Integer> ordinals = toSet(prefixIndex.findKeysWithPrefix("kea"));
        Assert.assertTrue(ordinals.size() == 1);
    }