SolidTut-code-suggestion

    public function upload(): string
    {
        if (strtolower($_SERVER['REQUEST_METHOD']) !== 'post') {
            return $this->render($this->showForm());
        }

        if (!array_key_exists('newPicture', $_FILES) || !array_key_exists('author', $_POST)) {
            return $this->error400();
        }
        
        // Process form
        return $this->render(
            $this->storeUploadedPicture(
                $_FILES['newPicture'],
                $_POST['author'],
                $_POST['location']
            )
        );
    }