Action.sendGoal(): Why is resultCallback required?

[ikwilnaarhuisman]

Hi! Right now I'm working on implementing a Charge Action, when I want my robot to charge I send it a goal using this Action. This works great, but I'm forced to define a resultCallback. The thing is that I use a different topic to determine whether the robot went to charge or not. So I don't have any use for the callback on this Goal.

I'm just wondering why resultCallback isn't allowed to be undefined like feedbackCallback and feedbackCallback?