Arrays.<@Nullable String>asList("a", null, "b").iterator();
    assertThrows(
        NullPointerException.class, () -> ImmutableMultiset.copyOf((Iterator<String>) iterator));
  }

  public void testToImmutableMultiset() {
    BiPredicate<ImmutableMultiset<String>, ImmutableMultiset<String>> equivalence =
        (ms1, ms2) -> ms1.equals(ms2) && ms1.entrySet().asList().equals(ms2.entrySet().asList());