Question
How to see if the "Read Data" element will return something? The read data seems to return 00000000-0000-0000-0000-000000000000 for the Uid when it doesn't get anything.
Answer
If you try to fetch a GUID within the business process that does not exist it will be automatically populated with 0's. The easiest way to check the value of the retrieved UID would be adding an auto-generated page after the desired element, that would return the value you were trying to fetch.