...

BEGIN TRY
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    SELECT
        NoteId,
        Url,
        Subject,
        Content,
        ExpiresAt,
        RemindAt
    FROM dbo.browsingnotes_Notes
    WHERE UserId = @UserId
        AND Hash = @Hash
END TRY
BEGIN CATCH
    SELECT
        NULL AS 'NoteId',
        NULL AS 'Url',
        NULL AS 'Subject',
        NULL AS 'Content',
        NULL AS 'ExpiresAt',
        NULL AS 'RemindAt'
END CATCH

THROW [ { error_number | @local_variable },
        { message | @local_variable },
    { state | @local_variable }
] [ ; ]

SELECT
    NoteId,
    Url,
    Subject,
    Content,
    ExpiresAt,
    RemindAt
FROM dbo.browsingnotes_Notes
WHERE UserId = @UserId
    AND Hash = @Hash
union
select NULL, NULL, NULL, NULL, NULL, NULL
  where not exists ( select 42 from dbo.browsingnotes_Notes where UserId = @UserId and Hash = @Hash )