主动加载在一对多关系上返回null

我有三个表，它们有多对多的关系表名:notes(id,user_id,card_id,body)， Users(id,name,password，…)，Card(id,cardname,cardText)现在我想使用即时加载来获取相关的用户名我有三个模型，如下所示:

<?php
namespace App;
use Illuminate'Database'Eloquent'Model;
class Card extends Model
{
    /*public $table= 'Fake';*/
    public $timestamps = false;
    public function notes()
    {
        return $this->hasMany(Note::class);
    }
}
<?php
namespace App;
use Illuminate'Database'Eloquent'Model;
class Note extends Model
{
    public $timestamps = false;
    public function cards()
    {
        return $this->belongsTo(Card::class);
    }
    public function users()
    {
        return $this->belongsTo(User::class);
    }
}
<?php
namespace App;
use Illuminate'Database'Eloquent'Model;
class User extends Model
{
    public $timestamps = false;
    public function notes()
    {
        return $this->hasMany(Note::class);
    }
}

，在我的路由中，我使用如下:

<?php
use App'Card;
Route::get('/', function () {
    $card=new Card();
    $card->id=1;
    $card->load('notes.users')->all();
    return $card;
});

，但我不知道为什么我得到空用户在json:json文件:

{
id: 1,
notes: [
{
id: 1,
card_id: 1,
user_id: 1,
body: "Hussein Jafari",
users: null
},
{
id: 2,
card_id: 1,
user_id: 1,
body: "Ammpeaa",
users: null
},
{
id: 12,
card_id: 1,
user_id: 1,
body: "KAIRIMI SANJABI",
users: null
},
{
id: 13,
card_id: 1,
user_id: 1,
body: "MOAHAHS KASK KSK",
users: null
},
{
id: 14,
card_id: 1,
user_id: 1,
body: "bENAJAJ KSAK KS",
users: null
}
]
}