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
seDT = findDesignTimeSeries( seRT ); 
								List components = (List)componentPrimitives.get(seDT);
								if (components != null){
									Iterator iter = components.iterator();
									StringBuffer sb = new StringBuffer();
									sb.append(seDT.hashCode());
									if (iter.hasNext())
										sb.append(",new Array(");							 
									while (iter.hasNext()){
										sb.append("'").append(iter.next()).append("'"); 
										if (iter.hasNext())
											sb.append(","); 
									}
									if (components.size() > 0)
										sb.append(")"); 
									elm.setAttribute(scriptEvent, 
											"highlight(evt, " 
													+ sb.toString() + ")"); 							
									setCursor(elm);
		
									
									((SVGGraphics2D)_g2d).addCSSStyle(".class"+seDT.hashCode(), "visibility", "visible"); 
								}
							}
							catch ( ChartException oosx )
							{
								logger.log( oosx );
								return;
							}
						}