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Map.get() may return null.

Check for null.

• missing/condition/null_check

org/jfree/chart/plot/CategoryPlot.java

removeDomainMarker(int, Marker, Layer, boolean)

class CategoryPlot {
    /**
     * Removes a marker for a specific dataset/renderer and, if requested, 
     * sends a {@link PlotChangeEvent} to all registered listeners.
     *
     * @param index the dataset/renderer index.
     * @param marker the marker.
     * @param layer the layer (foreground or background).
     *
     * @return A boolean indicating whether or not the marker was actually 
     *         removed.
     *
     * @since 1.0.10
     */
    public boolean removeDomainMarker(int index, Marker marker, Layer layer,
    		boolean notify) {
        ArrayList markers;
        if (layer == Layer.FOREGROUND) {
            markers = (ArrayList) this.foregroundDomainMarkers.get(new Integer(
                    index));
        }
        else {
            markers = (ArrayList) this.backgroundDomainMarkers.get(new Integer(
                    index));
        }
        boolean removed = markers.remove(marker);
        if (removed && notify) {
            fireChangeEvent();
        }
        return removed;
    }

}