The biggest question for me here is whether it's sensible for API authors to even provide a default in this case or instead require that argument is always specified explicitly if there are multiple possible choices, like with this Void example for Pitch: Allow functions with void-params to be called as void-functions - the choice, it seems, is to provide default only if there is no output to improve ergonomics of that API, it doesn't means that send() should be supported for every possible Output.