public Set<ContentPack> findAllById(ModelId id) {
        final DBCursor<ContentPack> result = dbCollection.find(DBQuery.is(Identified.FIELD_META_ID, id));
        return ImmutableSet.copyOf((Iterable<ContentPack>) result);
    }
@Test
    @MongoDBFixtures("ContentPackPersistenceServiceTest.json")
    public void findAllByIdWithInvalidId() {
        final Set<ContentPack> contentPacks = contentPackPersistenceService.findAllById(ModelId.of("does-not-exist"));

        assertThat(contentPacks).isEmpty();
    }