Undefined variable by using eloquent relationships

Here is the error returned by Laravel :

ErrorException compact(): Undefined variable $lists

I am trying to join multiples tables like :
Tops has many Lists and Lists has many Medias

I have this code in my TopController :

 $tops = Top::with(
                    'user:id,name,email',
                    'lists:id',
                    'categories:title,slug'
                )->paginate(20); 

I have no problem for retrieve user and categories datas but the lists variable seems to be undefined and I do not understand why.

Here is the Liste.php Model :

 public function user()
    {
        return $this->belongsTo(User::class);
    }


      public function tops()
    {
        return $this->belongsToMany(Top::class);
    }



      public function medias()
    {
        return $this->belongsToMany(Medias::class);
    }

Thank you for your help.

https://pastebin.com/Anv4AhVe

>Solution :

you just need to define a $lists variable in your index method.