laravel belongsTo gives null

belongsTo relation in laravel is returning null

public function games(){
    return $this->belongsTo('App\Models\Game');
  }

but when i provide key as argument it seems to work fine

  public function games(){
        return $this->belongsTo('App\Models\Game','game_id');
      }

but as per the docs game_id is itself is a default argument. What is the small thing i am missing here.

Thanks

via Chebli Mohamed