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
are.getTopLeft( ).getY( )
								+ ( are.getHeight( ) - 2 * are.getInnerRadius( ) )
								/ 2,
						2 * are.getInnerRadius( ),
						2 * are.getInnerRadius( ),
						are.getStartAngle( ),
						are.getAngleExtent( ),
						Arc2D.PIE );
				Area fArea = new Area( outerArc );
				fArea.exclusiveOr( new Area( innerArc ) );
				elm = svggc.createGeneralPath( fArea );
			}
			else
			{
				elm = svggc.createGeneralPath( new Arc2D.Double( are.getTopLeft( ).getX( ),
						are.getTopLeft( ).getY( ),
						are.getWidth( ),
						are.getHeight( ),
						are.getStartAngle( ),
						are.getAngleExtent( ),
						toSwingArcType( are.getStyle( ) ) ) );
			}
			
		}
		
		
		
		
		
		if (elm != null) {