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
return;
		}		
		SVGGraphics2D svg_g2d = (SVGGraphics2D)_g2d;
		
		
		
		if (pre.getSource() instanceof StructureSource) {
			final StructureSource src = isSeries((StructureSource) pre.getSource( ));
			if ( src != null ){
				if (!drawText)
					svg_g2d.setDeferStrokColor(null);
				svg_g2d.popParent();
			}
		}
	}
	
	public void drawArc(ArcRenderEvent are) throws ChartException {
		groupPrimitive(are, false);
		super.drawArc(are);
		ungroupPrimitive(are, false);
	}
	public void drawArea(AreaRenderEvent are) throws ChartException {
		groupPrimitive(are, false);
		super.drawArea(are);
		ungroupPrimitive(are, false);
	}
	public void drawImage(ImageRenderEvent pre) throws ChartException {
		groupPrimitive(pre, false);
		super.drawImage(pre);
		ungroupPrimitive(pre, false);