framework/web/CacheSession.php
public function readSession($id)
    {
        $data = $this->cache->get($this->calculateKey($id));

        return $data === false ? '' : $data;
    }
public function readSession($id)
    {
        $data = $this->cache->get($this->calculateKey($id));

        return $data === false ? '' : $data;
    }
Session read handler.
@internal Do not call this method directly.
@param string $id session ID
@return string the session data