Pivot model can't have belongsToMany other model

[TutanRamon]

• Laravel Version: 7.13.0
• PHP Version: 7.3.2
• Database Driver & Version: MariaDB 10.1.3.8

Description:

I have a model Article and a model Site. I also have a combined model ArticleSite (pivot). I also have a model Dossier (these are kinds op tags you can attach to an ArticleSite). So, I needed a many-2-many between Dossier and ArticleSite. When I manually insert some records into my database, I can fetch the Dossiers linked to ArticleSite within an collection, but saving keeps getting errors, like:
SQLSTATE[42S22]: Column not found: 1054 Unknown column '' in 'field list (SQL: insert into 'article_site_dossier' ('', 'dossier_id') values (?, 1))

Steps To Reproduce:

ArticleSite pivot model:

class ArticleSite extends Pivot
{
	protected $primaryKey = 'id';

	public function dossiers()
	{
		return $this->belongsToMany('App\Dossier', 'article_site_dossier');
	}

	public function article()
	{
		return $this->belongsTo('App\Article');
	}
}

Dossier model

use Illuminate\Database\Eloquent\Model;

class Dossier extends Model
{
	public function articleSites()
	{
		return $this->belongsToMany('App\ArticleSite', 'article_site_dossier', 'dossier_id', 'articlesite_id');
	}

	public function site()
	{
		return $this->belongsTo('App\Site');
	}
}

I have a simple function in my web file to test the functionality:

Route::get('/testget', function () {
	$test = ArticleSite::with('dossiers', 'article','article.user')->get();
	dd($test);
});

This works fine.

What does not work, is this:

Route::get('/testpost', function () {

	$article 				= new Article();
	$article->title 		         = "Test 2";
	$article->user_id 		= 1;
	$article->contents		= "Lorem ipsum Lorem ipsum Lorem ipsum Lorem ipsum Lorem ipsum ";

	$article->save();

	$articleSite 				= new ArticleSite();
	$articleSite->article_id 	= $article->id;
	$articleSite->site_id		= 1;
	$articleSite->category_id = 1;

	$articleSite->save();

	$dossier = Dossier::find(1);

	$articleSite->dossiers()->attach($dossier);

	
});

I skipped some fields for readabilty. The following line results in the error I posted earlier.
$articleSite->dossiers()->attach($dossier);

I also tried the sync method. I tried defining the fields on the relation, but i keeps posting a null value and empty column name. Is this a bug or I am implementing it incorrectly?

EDIT:
migration for ArticleSite pivot model:

public function up()
	{
		Schema::create('article_site_dossier', function (Blueprint $table) {
			$table->bigIncrements('id');

			$table->bigInteger('articlesite_id')->unsigned();
			$table->bigInteger('dossier_id')->unsigned();
			$table->timestamps();

			$table->foreign('articlesite_id')->references('id')->on('article_site');
			$table->foreign('dossier_id')->references('id')->on('dossiers');
		});
	}

[TutanRamon]

Ok, I solved it.
I just changed
class ArticleSite extends Pivot

to
class ArticleSite extends Model

Feels kind of odd though...