private Object readResolve() throws ObjectStreamException {
        if (this.equals(DomainOrder.ASCENDING)) {
            return DomainOrder.ASCENDING;
        }
        else if (this.equals(DomainOrder.DESCENDING)) {
            return DomainOrder.DESCENDING;
        }
        else if (this.equals(DomainOrder.NONE)) {
            return DomainOrder.NONE;
        }
        return null;