Merge branch 'educoder' into develop

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