i had to wrap you r example a couple of times to get it to return an empty string instead of null;

does this help at all?

declare @id int

set @id = null

SELECT ISNULL(NULLIF(convert(varchar(max),Results),'<ID/>'),'') As Val

FROM

(

SELECT Results =(

SELECT

CASE WHEN @id is null

THEN null

ELSE 'Forehead Barcode' END

AS [IDType],

RTRIM(@id) as [Value]

FOR XML PATH('ID'), TYPE)

)x