checkUnmodifiableMultimap(TreeMultimap.<String, Integer>create(), false, "null", 42);
  }

  @J2ktIncompatible
  @GwtIncompatible // SerializableTester
  public void testSerializingUnmodifiableTreeMultimap() {
    Multimap<String, Integer> unmodifiable =
        prepareUnmodifiableTests(TreeMultimap.<String, Integer>create(), false, "null", 42);
    SerializableTester.reserializeAndAssert(unmodifiable);
  }