diff --git a/app/logical/post_sets/base.rb b/app/logical/post_sets/base.rb
index 6dd73cbcb..e8bdb5bad 100644
--- a/app/logical/post_sets/base.rb
+++ b/app/logical/post_sets/base.rb
@@ -20,6 +20,10 @@ module PostSets
       false
     end
 
+    def tag_string
+      nil
+    end
+
     def presenter
       raise NotImplementedError
     end