@Test
  public void clear() throws Exception {
    String id = "i1";
    ImmutableItem item = ImmutableItem.builder().id(id).addList("l1").build();
    repository.upsert(item).getUnchecked();

    repository.update(repository.criteria().id(id))
        .clearList()
        .updateFirst()
        .getUnchecked();

    check(findById(id).list()).isEmpty();
  }
Checks {@code $push} functionality of repository
mongo/test/org/immutables/mongo/fixture/SimpleUpdaterTest.java