public function getAttribute($key)
    {
        if (isset($this->mutations[$key]))
        {
            return $this->mutations[$key];
        }

        if (array_key_exists($key, $mutatables = static::getMutatables()))
        {
            return $this->mutateExtensionAttribute($key, $mutatables[$key]);
        }

        return parent::getAttribute($key);
    }