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
if ( ( (DataSetItemModel) dataSetItemModel ).getDataSetColumnName( )
						.equals( keyChooser.getText( ) ) )
					return DataType.getClass( ( (DataSetItemModel) dataSetItemModel ).getDataType( ) );
			}
		}
		return null;
	}
	/**
	 * Reset intervalType
	 * 
	 * @param choice
	 */
	private void resetIntervalType( IChoice[] choice )
	{
		intervalType.removeAll( );
		for ( int i = 0; i < choice.length; i++ )
		{
			intervalType.add( choice[i].getDisplayName( ) );
		}
		intervalType.setData( choice );
		intervalType.select( 0 );
		intervalType.addSelectionListener( new SelectionAdapter( ) {
			public void widgetSelected( SelectionEvent e )
			{
				intervalRange.setEnabled( intervalType.getSelectionIndex( ) != 0 );
				intervalBaseButton.setEnabled( intervalType.getSelectionIndex( ) != 0
						&& ( getColumnType( ) != String.class ) );
				intervalBaseText.setEnabled( intervalBaseButton.getEnabled( )
						&& intervalBaseButton.getSelection( ) );
			}