Comparator<? super E> comparator = (Comparator<? super E>) requireNonNull(stream.readObject());
    deserializationReplacement = new TreeMultiset<>(comparator);
    Serialization.populateMultiset(deserializationReplacement, stream);
  }

  @J2ktIncompatible
  @GwtIncompatible
    private Object readResolve() {
    return requireNonNull(deserializationReplacement); // set by readObject
  }