Bug 317267 [Automation][Regression]Error is thrown out when preview gantt type chart
chart/org.eclipse.birt.chart.engine.extension/src/org/eclipse/birt/chart/extension/datafeed/GanttDataSetProcessorImpl.java
{
		if ( columnData == null || columnData.length == 0 )
		{
			throw new ChartException( ChartEngineExtensionPlugin.ID,
					ChartException.DATA_SET,
					"exception.base.orthogonal.null.datadefinition", 
					Messages.getResourceBundle( getULocale( ) ) );
		}
		StringBuffer buffer = new StringBuffer( );
		for ( int i = 0; i < columnData.length; i++ )
		{
			if ( columnData[i] == null )
			{
				throw new ChartException( ChartEngineExtensionPlugin.ID,
						ChartException.DATA_SET,
						"exception.base.orthogonal.null.datadefinition", 
						Messages.getResourceBundle( getULocale( ) ) );
			}
			if ( columnData[i] instanceof Object[] )
			{
				buffer.append( toGanttString( (Object[]) columnData[i] ) );
			}
			if ( i < columnData.length - 1 )
			{
				buffer.append( "," ); 
			}
		}
		return buffer.toString( );
	}
	private StringBuffer toGanttString( Object[] ganttArray )