在php5.6中获取错误不在php5.5中

Question

I'm trying to get a phpdaemon running on ubuntu 16.04 with php5.6. It runs on ubuntu 1404 with php5.5.9. I tried google of course but I don't know php code at all.

This is the error I'm getting:

PHP Warning:  array_key_exists() expects parameter 2 to be array, null given in /../../Service.php on line 79

This is the the actual code on line 79 an a bit below:

            if(array_key_exists("session_id", $createSession)) {
            // Session ID.
            $sessionId = $createSession["session_id"];

Would be great if someone could help me out.

EDIT: thanks for the quick replies. someone asked for the $createsession. I think this is it, but I am not sure. still, I'm not sure why it runs on the old version.

            // Create and invoke.
        $createSession = $this->call_service(P_XMLRPC_URL, "create_session", array(
            "requester" => $sale['prkcode'] . '#' . $sale['pdcode'],
            "service" => P_SERVICE,
            "version" => P_VERSION,
            "invoke" => array(
                "method" => PRM_INVOKE_METHOD,
                "parameters" => array(
                    "tickets" => array(
                        $ticket
                    )
                )
            )
        ));