public void addSeries(TimeSeries series) {
        if (series == null) {
            throw new IllegalArgumentException("Null 'series' argument.");
        }
        this.data.add(series);
        series.addChangeListener(this);
        fireDatasetChanged();
    }

    /**
     * Removes the specified series from the collection and sends a 
     * {@link DatasetChangeEvent} to all registered listeners.
     *
     * @param series  the series (<code>null</code> not permitted).
     */
    public void removeSeries(TimeSeries series) {
        if (series == null) {
            throw new IllegalArgumentException("Null 'series' argument.");
        }
        this.data.remove(series);
        series.removeChangeListener(this);
        fireDatasetChanged();
    }

    /**
     * Removes a series from the collection.
     *
     * @param index  the series index (zero-based).
     */
    public void removeSeries(int index) {
        TimeSeries series = getSeries(index);
        if (series != null) {
            removeSeries(series);