testing github.com/google/jsonapi - relation's attributes not populated from included data

jsonapi-test1.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"

	"github.com/google/jsonapi"
)

type Author struct {
	ID        string  `jsonapi:"primary,authors"`
	FirstName string  `jsonapi:"attr,first_name"`
	LastName  string  `jsonapi:"attr,last_name"`
	Posts     []*Post `jsonapi:"relation,posts"`
}

type Post struct {
	ID    string `jsonapi:"primary,posts"`
	Title string `jsonapi:"attr,title"`
	Text  string `jsonapi:"attr,text"`
}

func logError(err error) {
	if err != nil {
		fmt.Print("[Error] ")
		fmt.Println(err)
	}
}

func main() {
	authorJsonApi := []byte(`{
	    "data": {
		"id":"123",
		"type":"authors",
		"attributes": {
		    "first_name": "John",
		    "last_name": "Doe"
		},
		"relationships": {
		    "posts": {
			"data": [{
				"id": "456",
				"type": "posts"
			}],
			"links": {
			    "self": "http://example.com/api/authors/123/posts",
			    "related": "http://example.com/api/authors/123/relationships/posts"
			}
		    }
		},
		"links": {
		    "self": "http://example.com/api/authors/123"
		},
		"meta": {
		    "includes": ["posts"],
		    "duration": 600
		},
		"included":[{
		    "id":"456",
		    "type":"posts",
		    "attributes": {
			"title":"Foo",
			"text":"bar baz boo!"
		    }
		}]
	    }
	}`)
	fmt.Printf("%s\n", authorJsonApi)
	reader := bytes.NewReader(authorJsonApi)

	author := Author{}
	logError(jsonapi.UnmarshalPayload(reader, &author))
	fmt.Printf("%#v\n", author)
	fmt.Printf("%#v\n", *author.Posts[0])

	aJsonApi, err := jsonapi.MarshalOne(&author)
	logError(err)
	aJson, err := json.Marshal(&aJsonApi)
	logError(err)
	fmt.Printf("%s\n", aJson)
}