unmarshal "" into a *string leaves it as nil instead of an empty string

package main

import "launchpad.net/goyaml"
import "fmt"

func main() {
 s := ""
 mp := &s
 data, _ := goyaml.Marshal(mp)
 fmt.Printf("%s\n", string(data))
 var s2 *string
 goyaml.Unmarshal(data, &s2)
 if s2 != nil {
  fmt.Printf("%v, %q\n", s2, *s2)
 } else {
  fmt.Printf("%v\n", s2)
 }
}

actual output:
""

<nil>

expected output:
""

0xc20003b1c0, ""