private Object readResolve() throws ObjectStreamException {
        if (this.equals(ChartChangeEventType.GENERAL)) {
            return ChartChangeEventType.GENERAL;
        }
        else if (this.equals(ChartChangeEventType.NEW_DATASET)) {
            return ChartChangeEventType.NEW_DATASET;
        }
        else if (this.equals(ChartChangeEventType.DATASET_UPDATED)) {
            return ChartChangeEventType.DATASET_UPDATED;
        }
        return null;