SoapServer response null in Phalcon

when i run url https://localhost/NewApp/sms/test?wsdl to show xml in file wsdl , return null. Then I write file test.php in folder public and run https://localhost/test.php?wsdl . it return xml in file smssoap.wsdl This is my code :

public function testAction()

{
    ini_set("soap.wsdl_cache_enabled", "0");
    $soapServer = new \SoapServer('smssoap.wsdl', ["soap _version" => SOAP_1_2]);
    $soapServer->setObject($this);
    $soapServer->handle();
}

file test.php

<?php
class SmsSoapController{
        public function executeReceiveMO(){
            error_reporting(E_ALL);
            ini_set('display_errors', 1);
            ini_set("soap.wsdl_cache_enabled", "0"); // disabling WSDL cache
            $soap_server = new SoapServer('smssoap.wsdl',array('soap_version' => SOAP_1_2));
            $soap_server->setObject($this);
            $soap_server->handle();
            exit();
        }
}
$soap = new SmsSoapController();
$soap->executeReceiveMO();
?>