If someone creates an entry in update block like the second one in the screenshot with Source expression empty (not even two single quotes) then the update block goes on and on without any error message.
Is this a bug?
It would be really nice if Adobe Campaign Classic shows some error message in journal.
irrespective of what you update in that column if there is no outgoing transisiton , I believe you are going to get that but the workflow status changes to finished. you can do something like mentioned below and add END activity at the end if you dont want the activity to go on and on.