Review

Map.get() may return null.

Check for null.

• missing/condition/null_check

org/jfree/chart/plot/CategoryPlot.java

removeRangeMarker(int, Marker, Layer, boolean)

class CategoryPlot {
    /**
     * Removes a marker for a specific dataset/renderer and 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).
     * @param notify  notify listeners.
     *
     * @return A boolean indicating whether or not the marker was actually 
     *         removed.
     *
     * @since 1.0.10
     * 
     * @see #addRangeMarker(int, Marker, Layer, boolean)
     */
    public boolean removeRangeMarker(int index, Marker marker, Layer layer,
    		boolean notify) {
        if (marker == null) {
            throw new IllegalArgumentException("Null 'marker' argument.");
        }
        ArrayList markers;
        if (layer == Layer.FOREGROUND) {
            markers = (ArrayList) this.foregroundRangeMarkers.get(new Integer(
                    index));
        }
        else {
            markers = (ArrayList) this.backgroundRangeMarkers.get(new Integer(
                    index));
        }

        boolean removed = markers.remove(marker);
        if (removed && notify) {
            fireChangeEvent();
        }
        return removed;
    }

}

class CheckMarkersForNull {
  void pattern(Map foregroundDomainMarkers, int index, Marker marker) {
    ArrayList markers = (ArrayList) foregroundDomainMarkers.get(new Integer(index));
    if (markers != null) {
      markers.remove(marker);
    }
  }
}