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 testMovieActorMapReference() throws Exception {
        Map<Integer, Actor> idActorMap = new HashMap<>();
        idActorMap.put(1, new Actor("Keanu Reeves"));
        idActorMap.put(2, new Actor("Laurence Fishburne"));
        idActorMap.put(3, new Actor("Carrie-Anne Moss"));
        MovieActorMapReference movieActorMapReference = new MovieActorMapReference(1, 1999, "The Matrix", idActorMap);
        objectMapper.add(movieActorMapReference);
        StateEngineRoundTripper.roundTripSnapshot(writeStateEngine, readStateEngine);
        HollowPrefixIndex prefixIndex = new HollowPrefixIndex(readStateEngine, "MovieActorMapReference", "idActorNameMap.value");
        Set<Integer> ordinals = toSet(prefixIndex.findKeysWithPrefix("carr"));
        Assert.assertTrue(ordinals.size() == 1);
        ordinals = toSet(prefixIndex.findKeysWithPrefix("aaa"));
        Assert.assertTrue(ordinals.size() == 0);
    }