private Object readResolve() throws ObjectStreamException {
        if (this.equals(RangeType.FULL)) {
            return RangeType.FULL;
        }
        else if (this.equals(RangeType.POSITIVE)) {
            return RangeType.POSITIVE;
        }
        else if (this.equals(RangeType.NEGATIVE)) {
            return RangeType.NEGATIVE;
        }
        return null;