Bug 124777 Set blank tooltip in chart title will cause exception when preview.
Description: Set blank tooltip in chart title will cause exception when preview. Steps to reproduce: 1. New a simple chart 2. Add title interactivity: mouse over/show tooltip, keep tooltip text blank and click Add button. 3. Preview the chart in viewer and move mouse over the chart title. Expected result: Nothing happen. Actual result: Unexpected exception dialog poped up.
chart/org.eclipse.birt.chart.device.svg/src/org/eclipse/birt/chart/device/svg/SVGRendererImpl.java
*/
	protected void groupPrimitive(PrimitiveRenderEvent pre, boolean drawText) {
		if ( _iun == null )
		{
			logger.log( ILogger.WARNING,
					Messages.getString( "exception.missing.component.interaction", getLocale( ) ) ); 
			return;
		}		
		SVGGraphics2D svg_g2d = (SVGGraphics2D) _g2d;
		
		if (pre.getSource() instanceof StructureSource) {
			final StructureSource src = isSeries((StructureSource) pre
					.getSource());
			if (src != null) {
				try {
					Series seDT = findDesignTimeSeries((Series) src.getSource()); 
					String id = Integer.toString(pre.hashCode());
					
					List components = (List) componentPrimitives.get(seDT);
					if (components == null) {
						components = new ArrayList();
						componentPrimitives.put(seDT, components);
					}
					
					
					String idTemp = id;
					int counter = 1;
					while (components.contains(idTemp)) {
						idTemp = id + "@" + counter; 
						counter++;