SQL Server 2012 :: List Catalog Reports With No Execution History Returns 0 Rows

comparing UNIQUEIDENTIFIER columns..This query returns several rows where the [ReportId] and [LastRunDate] columns are both NULL:

SELECT [c].[Name],[c].[ItemID],[xl].[ReportID]
, MAX([TimeStart]) [LastRunDate]
FROM [dbo].[Catalog] [c]
LEFT JOIN [dbo].[ExecutionLogStorage] [xl] on [c].[ItemID] = [xl].[ReportID]
WHERE [c].[Type] NOT IN (1,5) -- Not a folder or a data source!
group by [c].[Name],[c].[ItemID],[xl].[ReportID]
order by 4

However, trying to just list catalog reports with no execution history returns 0 rows, but I'm expecting it to return a row for every NULL [ReportId] from the above query:

SELECT *
FROM [dbo].[Catalog]
WHERE [Type] NOT IN (1,5) -- Not a folder or a data source!
AND [ItemID] NOT IN (SELECT [ReportID] FROM [dbo].[ExecutionLogStorage])

I even tried casting [ItemId] and [ReportId] columns in the 2nd query to VARCHAR(255), and still got no rows, but the following queries return 0 rows and 1 row (respectively).

select * from [dbo].[ExecutionLogStorage] where [ReportID] = '0BB2209C-7736-46C8-AD02-4614EBA4F0F1'
select * from [dbo].[Catalog] where [ItemID] = '0BB2209C-7736-46C8-AD02-4614EBA4F0F1'