diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 919e374b..3ec38cde 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -4340,7 +4340,7 @@ module ApplicationHelper
         candown = (attachment.is_public == 1 || attachment.is_public == true)
       end
     else
-      if attachment.container_type == "MarkDown" || attachment.container_type == "Shixun" || attachment.container_type == "Memo" || attachment.container_type == "Career" || attachment.container_type == "Exercise" || attachment.container_type == "ExerciseBank"
+      if attachment.container_type == "MarkDown" || attachment.container_type.nil? || attachment.container_type == "Shixun" || attachment.container_type == "Memo" || attachment.container_type == "Career" || attachment.container_type == "Exercise" || attachment.container_type == "ExerciseBank"
         candown = true
       end
     end