code: @SuppressWarnings("unchecked")
    public static ImmutableSetMultimap<Object, Object> instantiate(SerializationStreamReader reader)
        throws SerializationException {
      Comparator<Object> valueComparator = (Comparator<Object>) reader.readObject();
      ImmutableSetMultimap.Builder<Object, Object> builder = ImmutableSetMultimap.builder();
      if (valueComparator != null) {
        builder.orderValuesBy(valueComparator);
      }
      return (ImmutableSetMultimap<Object, Object>)
          Multimap_CustomFieldSerializerBase.instantiate(reader, builder);
    }
docs: Serialization type safety is at the caller's mercy.