$this->client->disconnect() cause 'Invalid function arguments provided'

[CoorFun]

I have a Mqtt client defined in a class entity like this:

Class demo
{
    private $client;

    /* constructor */
    function __construct($host, $port)
    {
        $client_id = SnipsUtils::generate_client_id();
        $this->client = new Mosquitto\Client('demo-client');
        $this->client->onConnect([$this, 'mqtt_on_connect']);
        $this->client->onDisconnect([$this, 'mqtt_on_disconnect']);
        $this->client->onSubscribe([$this, 'mqtt_on_subscribe']);
        //$this->client->onLog([$this, 'mqtt_on_log']);
        $this->client->onMessage([$this, 'mqtt_on_message']);
        try {
            $this->client->connect($host, $port, 60);
        } catch (Exception $e) {
            echo $e
        }
    }

    /* deconstructor */
    function __destruct()
    {
        $this->client->disconnect();
        unset($this->client);
    }

    function mqtt_on_connect() {}
    function mqtt_on_disconnect() {}
    function mqtt_on_subscribe() {}
    function mqtt_on_message() {}
}

This will trigger : PHP Fatal error: Uncaught Mosquitto\Exception: Invalid function arguments provided. in the destructor when calling $this->client->disconnect();. And the fact is that the client is disconnected successfully withmqtt_on_disconnect() function called.