protected function makeTransformerInstance($transformerClass)
    {
        if ($transformerClass instanceof TransformerAbstract) {
            return $transformerClass;
        }

        $instance = app($transformerClass);

        if ( ! ($instance instanceof TransformerAbstract)) {
            throw new \UnexpectedValueException("{$transformerClass} is not a TransformerAbstract");
        }

        return $instance;
    }