How to query data from two database (PeopleSoft and Microsoft SQL) into one power table

One follow up question on the dataset combine scripting.
If I have serial numbers in dataset1 that are not present in dataset2 I get an error that I believe is stating there are not values to match up to that serial number. Would there be a way to make the WHSDate blank if the serial number does not exist in dataset2? Hopefully this makes sense.
Error recieved:
image