注册成功后可能导致此错误的原因是什么？

Question

Fatal error: Call to a member function prepare() on null in /home/user/public_html/demo/core/class.general.php on line 315

Below is the line of codes:

//settings
    public function configInfo(){
        try {
            $stmt = $this->connect->prepare("SELECT * FROM configuration");
            $stmt->execute();
        }
        catch(PDOException $e){
            echo $e->getMessage();
        }           
        $matches = $stmt->fetch(PDO::FETCH_ASSOC);          
        return $matches;
    }