From bd0efb852551de021fd51c6436bdc2b213289c9a Mon Sep 17 00:00:00 2001
From: Guo Xiang Tan <tgx_world@hotmail.com>
Date: Tue, 1 Aug 2017 17:57:26 +0900
Subject: [PATCH] Fix the build.

---
 app/models/category_list.rb | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/app/models/category_list.rb b/app/models/category_list.rb
index 6e98f9bc0a..f3ae8a1d00 100644
--- a/app/models/category_list.rb
+++ b/app/models/category_list.rb
@@ -25,10 +25,16 @@ class CategoryList
     trim_results
 
     if preloaded_topic_custom_fields.present?
-      Topic.preload_custom_fields(
-        @categories.map(&:displayable_topics).flatten,
-        preloaded_topic_custom_fields
-      )
+      displayable_topics = @categories.map(&:displayable_topics)
+      displayable_topics.flatten!
+      displayable_topics.compact!
+
+      if displayable_topics.present?
+        Topic.preload_custom_fields(
+          displayable_topics,
+          preloaded_topic_custom_fields
+        )
+      end
     end
   end