如何使用反射访问地图的nil键？

I have a map that has a nil-keyed value:

mapp := map[interface{}]interface{}{
    nil: "a",
}

Accessing it's nil key's directly works:

fmt.Println("key[nil]:", mapp[nil])

But using reflection it doesn't - how to do this?

rmapp := reflect.ValueOf(mapp)
rkey := reflect.ValueOf(interface{}(nil))
rval := rmapp.MapIndex(rmapp.MapIndex(rkey))
fmt.Println("key[nil]:", rval)

Non-working code here:
https://play.golang.org/p/6TKN_tDNgV

The missing piece appears to have been the zero value of the map's key type, which is needed to access the nil key of the map.

refmap.MapIndex(reflect.Zero(refmap.Type().Key()))

playground example

Here's one way to create a reflect.Value for a nil value of type interface{}:

rkey := reflect.ValueOf(new(interface{})).Elem()

playground example