private function addTransformer(KeyTransformerInterface $keyTransformer)
    {
        $finds = array_filter($this->transformers, function ($transformer) use ($keyTransformer) {
            return (\get_class($transformer) === \get_class($keyTransformer));
        });

        if (\count($finds) < 1) {
            $this->transformers[] = $keyTransformer;
        }
    }