Object null when trying to send message

[madsongr]

I'm using Ratchet and I like its implementation. I'm trying to send a message to all clients connected using chat example class with MessageComponentInterface but I get a null object after executing php script.

chat class:

<?php

use Ratchet\ConnectionInterface;
use Ratchet\MessageComponentInterface;
use Ratchet\Server\IoServer;

require('../vendor/autoload.php');

class ChatServer implements MessageComponentInterface
{
    protected $clients;

    public function __construct()
    {
        $this->clients = new \SplObjectStorage;
    }

    public function onOpen(ConnectionInterface $conn)
    {
        $this->clients->attach($conn);
        $msg = "Connection established!\n";

        // send server log to shell
        echo $msg;
        $this->sendMessageToAll($msg);
    }

    public function onMessage(ConnectionInterface $from, $msg)
    {
        foreach ($this->clients as $client) {
            // if ($from != $client) {
            $client->send($msg);
            // }
        }
    }

    # new 
    public function sendMessageToAll($msg)
    {
        foreach ($this->clients as $client) {
            echo "Sending message to {$client->resourceId} \n";
            $client->send($msg);
        }
    }
    # /new 

    public function onClose(ConnectionInterface $conn)
    {
        $this->clients->detach($conn);
    }

    public function onError(ConnectionInterface $conn, Exception $e)
    {
        $conn->close();
    }
}

server.php

require('../vendor/autoload.php');
require('./chat.php');

$app = new Ratchet\App('localhost', 8080);
$app->route('/chat', new ChatServer, array('*'));
$app->route('/echo', new Ratchet\Server\EchoServer, array('*'));
$app->run();

notify.php

require('./chat.php');

$message = "sending message from registerEvent";
echo $message;

$conn = new ChatServer();
$res = $conn->sendMessageToAll($message);
echo '<br/>';
echo json_encode($res);

$res is null when I execute notify.php. I'm testing it separately because my goal is to send a message to all users connected when a new register is created in a database table.

Can you tell me how can I fix it to make it works properly according to my goal?