/**
     * returns user object from user ID stored in request parameter
     */
    private function getUserFromParameter(Pap_Contexts_Action $context) {
        $context->debug("    Trying to get affiliate from request parameter '".Pap_Tracking_ActionRequest::PARAM_ACTION_AFFILIATEID."'");

        $userId = $context->getAffiliateIdFromRequest();
        if($userId != '') {
            return $this->getCorrectUser($context, $userId, Pap_Common_Transaction::TRACKING_METHOD_FORCED_PARAMETER);
        }

        $context->debug("        Affiliate not found in parameter");
        return null;
    }