Bug 136027 [Smoke]the report with a gounp can not preview
Description: the report with a gounp can not preview Steps to reproduce: 1. new a datasource and a dataset 2. drag the dataset to the layout 3. Add a group on the table. save and preview. Actual result: "Error happened while running the report" is appeared.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/GroupDialog.java
*/
	private static IChoice[] getIntervalChoiceArray( String[] str )
	{
		List choiceList = new ArrayList( );
		for ( int i = 0; i < intervalChoicesAll.length; i++ )
		{
			for ( int j = 0; j < str.length; j++ )
			{
				if ( intervalChoicesAll[i].getName( ).equals( str[j] ) )
				{
					choiceList.add( intervalChoicesAll[i] );
					break;
				}
			}
		}
		IChoice[] choice = new IChoice[choiceList.size( )];
		return (IChoice[]) choiceList.toArray( choice );
	}
	/**
	 * Get columnDataType
	 * 
	 * @return
	 */
	private Class getColumnType( )
	{
		for ( int i = 0; i < columnList.size( ); i++ )
		{
			Object dataSetItemModel = columnList.get( i );
			if ( dataSetItemModel instanceof DataSetItemModel )
			{