BSON encoding issues with mgo

gistfile1.go

package main

import (
	"launchpad.net/mgo/v2"
	"launchpad.net/mgo/v2/bson"
)

type insertType struct {
	Foo bson.ObjectId `bson:"foo,omitempty"`
}

func main() {
	
	conn, _ := mgo.Dial("localhost")
	db := conn.DB("test")
	coll := db.C("mgotest")
	
	coll.Insert(&insertType{Foo: bson.NewObjectId()})
}