What version of Go are you using (go version)?

$ go version
go version go1.14.4 darwin/amd64

Does this issue reproduce with the latest release?

In current package documentation at https://golang.org/pkg/net/http/#example_ServeMux_Handle

What operating system and processor architecture are you using (go env)?

$ go env
GOARCH="amd64"
GOOS="darwin"

What did you expect to see?

Expected example to initiate http.ListenAndServe or equivalent with new ServeMux

package main

import (
	"fmt"
	"log"
	"net/http"
)

type apiHandler struct{}

func (apiHandler) ServeHTTP(http.ResponseWriter, *http.Request) {}

func main() {
	mux := http.NewServeMux()
	mux.Handle("/api/", apiHandler{})
	mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
		// The "/" pattern matches everything, so we need to check
		// that we're at the root here.
		if req.URL.Path != "/" {
			http.NotFound(w, req)
			return
		}
		fmt.Fprintf(w, "Welcome to the home page!")
	})
	log.Fatal(http.ListenAndServe(":8080", mux))
}

What did you see instead?

The example immediately exits without serving

package main

import (
	"fmt"
	"net/http"
)

type apiHandler struct{}

func (apiHandler) ServeHTTP(http.ResponseWriter, *http.Request) {}

func main() {
	mux := http.NewServeMux()
	mux.Handle("/api/", apiHandler{})
	mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
		// The "/" pattern matches everything, so we need to check
		// that we're at the root here.
		if req.URL.Path != "/" {
			http.NotFound(w, req)
			return
		}
		fmt.Fprintf(w, "Welcome to the home page!")
	})
}

I'd be happy to work on this for my first contribution if accepted