Pitch: Allow functions with void-params to be called as void-functions

[gwendal.roue (Gwendal Roué)]

@xedin, could this be handled with your Type inference from default expressions pitch?

struct PassthroughSubject<Output, Failure: Error> {
    fun send(_ value: Output = ()) { ... }
}

(Assuming PassthroughSubject did not already provide the naked send() as a specific overload.)