Bug 193467 URL hyperlink can't work in chart viewer
chart/org.eclipse.birt.chart.viewer/src/org/eclipse/birt/chart/viewer/internal/util/ChartImageManager.java
RunTimeContext rtc, IExternalContext externalContext,
			IStyleProcessor styleProc ) throws Exception
	{
		this.sessionId = sessionId;
		this.cm = chartModel;
		this.sExtension = outputFormat;
		this.evaluator = evaluator;
		this.styleProc = styleProc;
		if ( externalContext == null )
		{
			this.externalContext = new IExternalContext( ) {
				public Object getObject( )
				{
					
					return null;
				}
				public Scriptable getScriptable( )
				{
					
					return null;
				}
			};
		}
		else
		{
			this.externalContext = externalContext;
		}
		if ( rtc == null )
		{
			this.rtc = new RunTimeContext( );