Hi, I'm trying to understand and learn php, pdo and oop'ing. But on testing this class, I'm getting an error:

Fatal error: Uncaught Error: Call to a member function getAttribute() on null in C:\xampp2\htdocs\oly-app\includes\Db.class.php:218 Stack trace: #0 C:\xampp2\htdocs\oly-app\index.php(37): lib\Db->select('spelers', Array) #1 {main} thrown in C:\xampp2\htdocs\oly-app\includes\Db.class.php on line 218

The code on line 37 is:
$player = $db->select('players', ['id' => 4]);