出于某些原因，我得到了一个错误致命错误：当我执行以下调用时，对null上的成员函数prepare（）的调用：

include_once(createMySQL.php);
$mySql = new createMySQL();
$conn = $mySql->makeSQLConnection();
$entry = $conn->prepare("INSERT INTO thisTable (val1) VALUES (:val)");
$entry->bindParam(":val", $val);
$entry->execute();

这是我的createmysql类

class createMySQL{

    function makeSQLConnection(){
        $this->connect();
    }

    private function connect(){
        $name = "localhost";
        $db = "thisDatabase";
        $username = "root";
        $password = "";
        try{
            $conn = new PDO("mysql:host=$name; dbname=$db; charset=UTF8", $username, $password);
        }catch(PDOException $e){
            die("PDOException:" . $e->getMessage());
        }
        //echo "success";
        return $conn;
     }
}

我不确定为什么会出现以下错误。有人对此有什么见解吗？