diff --git a/app/models/topic_list.rb b/app/models/topic_list.rb
index 4e021e87369..1071f573741 100644
--- a/app/models/topic_list.rb
+++ b/app/models/topic_list.rb
@@ -77,7 +77,8 @@ class TopicList
   end
 
   def categories
-    @categories ||= topics.map { |t| [t.category, t.category.parent_category] }.uniq.flatten.compact
+    @categories ||=
+      topics.map { |t| [t.category, t.category&.parent_category] }.uniq.flatten.compact
   end
 
   def load_topics