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
}
	/**
	 * Creates an SVG document and assigns width and height to the root "svg"
	 * element.
	 * 
	 * @return Document the SVG document
	 * @throws Exception
	 */
	protected Document createSvgDocument( ) throws Exception
	{
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance( );
		DocumentBuilder builder;
		builder = factory.newDocumentBuilder( );
		DOMImplementation domImpl = builder.getDOMImplementation( );
		DocumentType dType = domImpl.createDocumentType( "svg", 
				SVG_VERSION, SVG_DTD );
		Document svgDocument = domImpl.createDocument( XMLNS, "svg", dType ); 
		svgDocument.getDocumentElement().setAttribute("xmlns", XMLNS);
		svgDocument.getDocumentElement().setAttribute("xmlns:xlink", XMLNSXINK);
		
		return svgDocument;
	}
	protected Document createSvgDocument( double width, double height )
			throws Exception
	{
		Document svgDocument = createSvgDocument( );
		svgDocument.getDocumentElement( ).setAttribute( "width", 
				Double.toString( width ) );
		svgDocument.getDocumentElement( ).setAttribute( "height", 
				Double.toString( height ) );