添加 url() 会破坏 hook_mail 实现

I'm writing a module in Drupal-7 that dynamically sends a one-time login link to guests. Everything fires fine until I add the link to the $message array, when it chokes. If I do a dpm($message) the link appears in the $message['body'] array, as I would expect. If I comment out the line with the url() function, everything works as it should. Why is php/Drupal choking on this silly little link?

/*
 * Implement hook_mail().
 */

function rsvp_mail($key, &$message, $params) {
    switch($key) {
      case "send invite" :
        $timestamp = REQUEST_TIME;
        $account = $params['account'];
        $message['subject'] = "And invitation for $account->name";
        $message['body'][] = 'Some body text.';
        $message['body'][] = 'Some more text!';
        //here's the line that's breaking my brain:
        $message['body'][] = url( 'http://wedding.juicywatermelon.com/rsvp/' . $account->uid . "/" . $timestamp . "/" . md5($account->pass . $timestamp) . "/" . 'user/' . $account->uid . '/edit/Wedding');             
        break;
    }
  }

ps - 为简洁起见，我有代码在单独的函数调用中生成链接并将其移至钩子实现.然而，这对行为没有影响.

function rsvp_mail_send($account) {
  $module = 'rsvp';
  $from = "email@gmail.com";
  $key = "send invite";
  $params['account'] = $account;
  $to = $account->mail;
  $language = language_default();
  $send = TRUE;
  $result = drupal_mail($module, $key, $to, $language, $params, $from, $send);
}