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
* All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http:www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 * IBM Corporation - initial API and implementation
 ***********************************************************************/
package org.eclipse.birt.chart.device.svg;
import java.awt.Image;
import java.awt.Shape;
import java.awt.geom.Arc2D;
import java.awt.geom.Area;
import java.awt.image.ImageObserver;
import java.io.FileOutputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.ResourceBundle;
import java.util.Vector;
import javax.swing.ImageIcon;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Transformer;