fix permalinks serializer with subfolder setups

app/serializers/permalink_serializer.rb

@@ -1,31 +1,34 @@
 class PermalinkSerializer < ApplicationSerializer
-  attributes :id, :url, :topic_id, :topic_title, :topic_url, :post_id, :post_url, :post_number, :post_topic_title, :category_id, :category_name, :category_url, :external_url
+  attributes :id, :url, :topic_id, :topic_title, :topic_url,
+             :post_id, :post_url, :post_number, :post_topic_title,
+             :category_id, :category_name, :category_url, :external_url
 
   def topic_title
-    object.try(:topic).try(:title)
+    object&.topic&.title
   end
 
   def topic_url
-    object.try(:topic).try(:url)
+    object&.topic&.url
   end
 
   def post_url
-    object.try(:post).try(:url)
+    # use `full_url` to support subfolder setups
+    object&.post&.full_url
   end
 
   def post_number
-    object.try(:post).try(:post_number)
+    object&.post&.post_number
   end
 
   def post_topic_title
-    object.try(:post).try(:topic).try(:title)
+    object&.post&.topic&.title
   end
 
   def category_name
-    object.try(:category).try(:name)
+    object&.category&.name
   end
 
   def category_url
-    object.try(:category).try(:url)
+    object&.category&.url
   end
 end