Return dummy info from laravel relationship

In laravel we specify foreign keys this way

public function creator() {
     return $this->belongsTo('App\Models\User', 'creator_id', 'id');
}

Is there some way to return dummy user ('system') when creator_id is null?

Reason: to display it in template.

For example:

If creator_id = 10 => creator = {id: 1, name: 'John'}

If creator_id = null => creator = {id: 0, name: 'system'}

via Jackson J