public function update()
 {
     static::$auth->mustBeAdmin();
     $thread = new Thread($_POST['id']);
     $thread->processArray($_POST);
     if (!$thread->isValid()) {
         $_SESSION['thread.form'] = $thread;
         header("Location: ./?page=thread.edit&id=" . $_POST['id']);
         exit;
     }
     if ($_FILES['poster']['error'] === UPLOAD_ERR_OK) {
         $thread->savePoster($_FILES['poster']['tmp_name']);
     } else {
         if (isset($_POST['remove-image']) && $_POST['remove-image'] === "TRUE") {
             $thread->poster = null;
         }
     }
     $thread->save();
     header("Location: ./?page=thread&id=" . $thread->id);
 }