diff --git a/classes/local/controllers/maintenance_static_page_generator.php b/classes/local/controllers/maintenance_static_page_generator.php
index d58e87b..986750a 100644
--- a/classes/local/controllers/maintenance_static_page_generator.php
+++ b/classes/local/controllers/maintenance_static_page_generator.php
@@ -128,7 +128,7 @@ class maintenance_static_page_generator {
                 continue;
             }
             $saved = $this->io->save_url_file($href);
-            if (is_null($saved['url'])) {
+            if (empty($saved['url'])) {
                 $url = $href; // Skipped, use original URL.
             } else {
                 $this->update_link_stylesheet_parse($saved['file'], dirname($href));
diff --git a/classes/local/controllers/maintenance_static_page_io.php b/classes/local/controllers/maintenance_static_page_io.php
index a5dbb40..eeafb53 100644
--- a/classes/local/controllers/maintenance_static_page_io.php
+++ b/classes/local/controllers/maintenance_static_page_io.php
@@ -213,7 +213,7 @@ class maintenance_static_page_io {
     /**
      * Saves the content of the URL into a file, returning the local filename.
      * @param string $url Input URL.
-     * @return string|null Output filename or null if skipped.
+     * @return array|null Output an array with the filename and url or null if skipped.
      */
     public function save_url_file($url) {
         global $CFG;