Bug 193287 Switch to gantt chart and return will pop up error[0602]
Description: Switch to gantt chart and return will pop up error[0602] Step: 1. New a report, datasource and dataset 2. Add a bar chart. 3. Drop a string row from dataset into Category (X) Series 4. Input 100 into Value (Y) Series 5. Switch to Select Chart Type 6. Change the type as Gantt and return to Bar chart Actual result: The error will pop up and said that "Unable to use a non-datetime data to render a datetime axis"
chart/org.eclipse.birt.chart.reportitem.ui/src/org/eclipse/birt/chart/reportitem/ui/ReportDataServiceProvider.java
catch ( SemanticException e )
		{
			ChartWizard.showException( e.getLocalizedMessage( ) );
		}
	}
	/**
	 * Generate computed columns for the given report item with the closest data
	 * set available.
	 * 
	 * @param handle
	 *            the handle of the report item. No aggregation created.
	 * 
	 * @return true if succeed,or fail if no column generated.
	 * @see DataUtil#generateComputedColumns(ReportItemHandle)
	 * 
	 */
	private List generateComputedColumns( ReportItemHandle handle )
			throws SemanticException
	{
		DataSetHandle dataSetHandle = handle.getDataSet( );
		if ( dataSetHandle == null )
		{
			dataSetHandle = DEUtil.getBindingHolder( handle ).getDataSet( );
		}
		if ( dataSetHandle != null )
		{
			List resultSetColumnList = DataUtil.getColumnList( dataSetHandle );
			ArrayList columnList = new ArrayList( );
			for ( Iterator iter = resultSetColumnList.iterator( ); iter.hasNext( ); )
			{