src/Alexa.php
public function session($key = null, $value = null)
    {
        if (!is_null($value)) {
            $this->setSession($key, $value);
        } elseif (is_null($key)) {
            return $this->session;
        } else {
            return array_key_exists($key, $this->session) ? $this->session[$key] : null;
        }
    }
public function session($key = null, $value = null)
    {
        if (!is_null($value)) {
            $this->setSession($key, $value);
        } elseif (is_null($key)) {
            return $this->session;
        } else {
            return array_key_exists($key, $this->session) ? $this->session[$key] : null;
        }
    }
@param string|null $key
@param mixed|null  $value

@return array|mixed|null