public function build()
    {
        if (!empty($this->container)) {
            return $this->container;
        }

        $contents = array_map(function ($containerBuilder) {
            return $containerBuilder->build();
        }, $this->containerBuilders);

        $this->container = [
            'type' => ContainerType::CAROUSEL,
            'contents' => $contents,
        ];

        return $this->container;
    }