bson.go
func (id *ObjectId) MarshalJSON() ([]byte, error) {
	var w jwriter.Writer
	id.MarshalEasyJSON(&w)
	return w.BuildBytes()
}
func (id *ObjectId) MarshalJSON() ([]byte, error) {
	var w jwriter.Writer
	id.MarshalEasyJSON(&w)
	return w.BuildBytes()
}
// MarshalJSON returns the ObjectId as JSON