Pathologic

<?php
if ($modx->event->name == 'OnWebPagePrerender') {
    $_url = parse_url($_SERVER['REQUEST_URI']);
	  if($modx->resource->isfolder && !preg_match("/\/$/", $_url['path'])) {
	      $id = $modx->resource->id;
		    $url = isset($_url['query']) ? $modx->makeUrl($id, '', $_url['query']) : $modx->makeUrl($id);
		    $modx->sendRedirect($url, ['responseCode' => 'HTTP/1.1 301 Moved Permanently']);
	  }
}