Why DefaultServeMux is selected as nil replacement in calls to Then?

[Komosa]

Additional question: why not do nothing handler?, like:

http.HandlerFunc(func(http.ResponseWriter, *http.Request) {})

[Justinas Stankevičius]

Hi,

This replicates the behavior seen in net/http.Serve() (or ListenAndServe()), which also substitutes nil with DefaultServeMux.

My other idea for handling nil was to panic, but this seemed like a less scary alternative and a nice shortcut for those using DefaultServeMux.

A do-nothing handler is, I think, a rare case and easy to spin-out yourself.