Why it returns null? .. PHP User class

i need your help. Today, i was doing this code for 3 hours and Im really desperate now.

I have got a class for login/register. I make it with a help of Youtube-tutorial. My problem is, my remember function doesnt work. Look at this.

  if($hashCheck->count()){
    $user = new User($hashCheck->first()->user_id);
    $user ->login();

  }

In this part i make a new User object, giving a number (ID) like a param.. Next thing i do is...

 public function __construct($user = null){
    $this->_db = DB::getInstance();
    $this->_sessionName = Config::get('session/session_name');
    $this->_cookieName = Config::get('remember/cookie_name');

    if(!$user){
        if(Sessio::exists($this->_sessionName)){
          $user = Sessio::get($this->_sessionName);

            if($this->find($user)){
                $this->_isLoggedIn = true;
            }
            else{
                //logout
            }
        }
        else{
            $this->find($user);
        }
    }
}

now, var_dump($user) returns null so next is if(!$user){}.. it tries to call function find.. This is my function find

 public function find($user = null){
    var_dump($user);

    if($user){
        echo'probiha find';
        $field = (is_numeric($user)) ? 'id' : 'jmeno';
        $data = $this->_db->get('uzivatele', array($field,'=',$user));
        if($data->count()){
            echo 'data count';
            $this->_data = $data->first();
            return true;
        }
    }
    return false;
}

But my $user is still null (and shoud be a number - ID)... When it is ID, function find will be work correct.

My question is, why is $user in construct null? :( When i done $user = new User($hashCheck->first()->user_id); it should be a number.. $hashCheck->first()->user_id returns a number (ID of user..) Thanks everybody for every answer :)