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
{
				intervalBaseButton.setEnabled( false );
				intervalBaseText.setEnabled( false );
			}
			else
			{
				intervalBaseButton.setEnabled( true );
				intervalBaseButton.setSelection( inputGroup.getIntervalBase( ) != null );
				intervalBaseText.setEnabled( intervalBaseButton.getSelection( ) );
				if ( inputGroup.getIntervalBase( ) != null )
				{
					intervalBaseText.setText( inputGroup.getIntervalBase( ) );
				}
			}
		}
		if ( inputGroup instanceof TableGroupHandle )
		{
			includeHeader.setSelection( inputGroup.hasHeader( ) );
			includeFooter.setSelection( inputGroup.hasFooter( ) );
		}
		else
		{
			includeHeader.setSelection( false );
			includeFooter.setSelection( false );
		}
		if ( DesignChoiceConstants.SORT_DIRECTION_ASC.equals( inputGroup.getSortDirection( ) ) )
		{
			ascending.setSelection( true );
		}
		else