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
sortPage.setInput( list );
		sortItem.setText( TAB_SORTING );
		sortItem.setControl( sortPage );
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.designer.internal.ui.dialogs.BaseDialog#initDialog()
	 */
	protected boolean initDialog( )
	{
		if ( inputGroup.getName( ) != null )
		{
			nameEditor.setText( inputGroup.getName( ) );
		}
		refreshColumnList( );
		setKeyExpression( inputGroup.getKeyExpr( ) );
		int index = getIntervalTypeIndex( inputGroup.getInterval( ) );
		intervalType.select( index );
		if ( index == 0 )
		{
			intervalRange.setEnabled( false );
			intervalBaseButton.setEnabled( false );
			intervalBaseText.setEnabled( false );
		}
		else
		{
			intervalRange.setEnabled( true );
			intervalRange.setSelection( inputGroup.getIntervalRange( ) );
			if ( getColumnType( ) == String.class )