RSS Link Fatal Error

I'm running Drupal 6.17, and I installed Featured Content 6.x-1.0-beta4. I configured a new featured content block with an RSS feed. Then, every time I requested a page on which this block was to be displayed, PHP stopped with this error:
Fatal error: Unsupported operand types in
/includes/common.inc on line 1430

I went to that location and found that the $options argument given at that call was NULL. So I added a debug_print_backtrace() and found this:
#0 url(featured-content/feed/1, ) called at [
/sites/all/modules/featured_content/featured_content.module:246]

The code around that location is this:

  // add rss link
  if ($featured_content['rss']['display']) {
    $settings['rss-link'] = theme('feed_icon', url('featured-content/feed/'.$delta, $query_string), 'RSS Feed');  // line 246
  }

The problem is that $query_string is never set before this line, so the module is calling url() with a NULL second argument, which incurs a fatal error.