Yes, i don't know why, but i created the first property, even knowing the category its required the property saved, but after that can't enter again in properties.

/mavitm/estate/realties

Trying to get property of non-object /plugins/mavitm/estate/models/Realty.php line 77

public function getCategoryNameAttribute(){
        return $this->category->title;
    }

If you want, i can do a pull request.