diff --git a/classes/search/activity.php b/classes/search/activity.php
index 1235776..631c020 100644
--- a/classes/search/activity.php
+++ b/classes/search/activity.php
@@ -67,6 +67,9 @@ class activity extends \core_search\base_activity {
     public function get_document($record, $options = []) {
         // Get the default implementation.
         $doc = parent::get_document($record, $options);
+        if (!$doc) {
+            return false;
+        }
 
         // Add the subtitle and additional info fields.
         $doc->set('description1', content_to_text($record->subtitle, false));