Today I attempted to use Tableau Prep 2018.3.2 to create a flow that would union, clean, and output a Hyper extract for four Microsoft Excel workbooks. However, I kept running into a problem at the output stage. Every time I tried running the flow to generate the Hyper extract I received the following generic error ("An error has occurred while running the flow."):
When looking at the notifications panel, I had hoped to see more information on what was causing the error, but no luck there either (another generic error... "System error: null"):
After some investigation (h/t: Bridget Cogley) I found that the changing of the data type for two fields (from Number to String) after the data was being unioned was causing the issue. When I moved these steps to complete before the data was unioned the Hyper extract was generated successfully and I regained my sanity.
Just thought I'd share. Hopefully, this explanation helps someone else.
Thanks for sharing, Alex