Bug 417317 Error when running chart example SwingInteractivityViewer.java.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/render/InteractiveRenderer.java
}
	private void hideLabel( PrimitiveRenderEvent event )
	{
		Label label = event.getLabel( );
		if ( label != null )
		{
			saveLabel( label );
			label.setVisible( false );
		}
	}
	public String getSource( StructureSource src )
	{
		if ( src.getType( ) == StructureType.SERIES
				|| src.getType( ) == StructureType.SERIES_DATA_POINT )
		{
			if ( isColoredByCategories( ) )
			{
				if ( src.getSource( ) instanceof DataPointHints )
				{
					DataPointHints hints = (DataPointHints) src.getSource( );
					int index = hints.getIndex( );
					return "category_" + String.valueOf( index ); 
				}
				else
					return null;
			}
			else
			{
				Series series;
				if ( src.getType( ) == StructureType.SERIES )