uniqueidentifier is a GUID and not a string so think you need to convert it to a string.
- MSDN docs for uniqueidentifier: https://docs.microsoft.com/en-us/sql/t-sql/data-types/uniqueidentifier-transact-sql?view=sql-server-ver15#examples
- Found this on Stackoverflow: https://stackoverflow.com/questions/6299918/sql-server-converting-uniqueidentifier-to-string-in-a-case-statement