diff --git a/app/models/attachment.rb b/app/models/attachment.rb
index a918f4e0a..292a409af 100644
--- a/app/models/attachment.rb
+++ b/app/models/attachment.rb
@@ -35,7 +35,7 @@ class Attachment < ApplicationRecord
 
   def title
     title = filename
-    if container.is_a?(StudentWork) && author_id != User.current.id
+    if container && container.is_a?(StudentWork) && author_id != User.current.id
       course = container&.homework_common&.course
       unless User.current.teacher_of_course?(course)
         title = "#{Time.now.strftime('%Y%m%d%H%M%S')}_#{DCODES.sample(8).join}" + File.extname(filename)