This kind of thing will help people get into Godot a lot I feel and it's nice to see other people have the same idea, I like you're showing multiple knockback styles too. I've got a plan myself to release a couple of projects I'm working on open source at a certain stage and they will be a turn based grand campaign style game and FPS/RPG. Show people exactly how to do specific mechanics and then people can use that as their templates for the projects they're working on to get a quick start on whatever game they like.
By the way, to solve the error it would just take throwing an if statement at it and then stopping the code.