db as a shared service not executed by Phalcon

When I set 'db' as a shared service, it is not executed by Phalcon ! But the connection to database is success. I don't know how !

My code:

services.php

$di->setShared('db', function () {
    $config = $this->getConfig();

    $class = 'Phalcon\Db\Adapter\Pdo\\' . $config->database->adapter;
    $params = [
        'host'     => $config->database->host,
        'username' => $config->database->username,
        'password' => $config->database->password,
        'dbname'   => $config->database->dbname,
        'charset'  => $config->database->charset
    ];

    if ($config->database->adapter == 'Postgresql') {
        unset($params['charset']);
    }

    $connection = new $class($params);
    return $connection;
});

bootstrap_web.php

<?php

use Phalcon\Di\FactoryDefault;
use Phalcon\Mvc\Application;

error_reporting(E_ALL);

define('BASE_PATH', dirname(__DIR__));
define('APP_PATH', BASE_PATH . '/app');

try {

    /**
     * The FactoryDefault Dependency Injector automatically registers the services that
     * provide a full stack framework. These default services can be overidden with custom ones.
     */
    $di = new FactoryDefault();

    /**
     * Include general services
     */
    require APP_PATH . '/config/services.php';

    /**
     * Include web environment specific services
     */
    require APP_PATH . '/config/services_web.php';

    /**
     * Get config service for use in inline setup below
     */
    $config = $di->getConfig();

    /**
     * Include Autoloader
     */
    include APP_PATH . '/config/loader.php';

    /**
     * Handle the request
     */
    $application = new Application($di);

    /**
     * Register application modules
     */
    $application->registerModules([
        'test' => ['className' => 'Project\Modules\Test\Module']
    ]);

    /**
     * Include routes
     */
//    require APP_PATH . '/config/routes.php';

    echo str_replace(["\n","\r","\t"], '', $application->handle()->getContent());

} catch (\Exception $e) {
    echo $e->getMessage() . '<br>';
    echo '<pre>' . $e->getTraceAsString() . '</pre>';
}

Am I doing something wrong ?