Hi Paul,
The out of the box node requires an applicable Function to be passed into the condition input to work. While the List.IsEmpty node returns a function, its condition isn’t met as the result will be True or False, and the List.Empty node doesn’t return a function as it has no input ports.
To solve this now, you can either use the Clockwork List.ReplaceEmptyLists node or approach 
Andreas’ approach is to convert first to a true/false boolean list and then replace those elements.
