Hi !
I tried your solution yesterday and it’s working fine.
To get rid out the the None
class, you have to handle all the stimuli and not only the first one ( get(0)). The first one appears to have a None class associated, but it’s not the case for the others 
We finally did it.
I’m now wondering if it is the good way to go. We are relying on an event (push) instead of asking at a fixed interval which actors are visible or heard (pull). If an event is missed, my AI will never know about it…