Memcached Adapter is not conforming to CacheAdapterInterface

[shehabic]

Environment

Sonata packages

$ composer show --latest 'sonata-project/*'
# Put the result here.

Symfony packages

$ composer show --latest 'symfony/*'
# Put the result here.

PHP version

$ php -v
# Put the result here.

Subject

Memcached Adapter is not conforming to CacheAdapterInterface the following:

    /**
     * {@inheritdoc}
     */
    public function get(array $keys)
    {
        return $this->handleGet($keys, $this->getCollection()->get($this->computeCacheKeys($keys)));
    }

should be:

    /**
     * {@inheritdoc}
     */
    public function get(array $keys): CacheElementInterface
    {
        return $this->handleGet($keys, $this->getCollection()->get($this->computeCacheKeys($keys)));
    }

Steps to reproduce

Just run anything that instantiates and uses Memcached Adapter, and you'll endup with Fatal Error for Php 7+

Expected results

Actual results