private function isExpandable(Model $model, $k, $value)
    {
        // if the value is falsey then do not expand it
        // could be null, excluded, or not included
        if (!$value) {
            return false;
        }

        // if not a property or no relationship model specified
        // then do not expand
        $property = $model::getProperty($k);
        if (!$property || !isset($property['relation'])) {
            return false;
        }

        return true;
    }