Overview page breaks <div> balance when there is no $vocab->description

function glossary_overview($vocab, $letter = null) {
  $dest = drupal_get_destination();
  $tbl = get_html_translation_table(HTML_SPECIALCHARS);
  $tbl[' '] = '_';
  $output = '<div id="'. strtr(drupal_strtolower($vocab->name), $tbl) .'">';
  if ($vocab->description) {
    $output .= '<p class="glossary-description">'. $vocab->description .'</p>';
  }
  else {
    $output = null;
  }

$output is being set. If there is a description, it is being added to, else it is nulled. At the end of this function, there is:

  return $output .'</div>';
}   

If there is no $vocab->description, there was no <div> set to close. I removed the else { } clause from this if { } and all is well for me.