Turns out that an empty tuple() definition mean nothing is passed in it. 
What I needed was the use of a Trigger device linked to the Target’s Hit Event and then I’d have access to the Agent… However, I also hit an issue with the optional / nullable parameter ?agent that was passed in…
I found my answer to that here: How do i convert from type ?agent to agent... im so confused with optionals - #3 by Twin01