diff --git a/.access_token b/.access_token
index 610b08d2e..2e228963c 100644
--- a/.access_token
+++ b/.access_token
@@ -1 +1 @@
-{"access_token":"oEEf8ZKAB8Y2G0o_xnTPkPJHKKk8iHkLC-f5ptvQ2nCMj9IpC86ivLD2-p38GfOkuG-HuQp3pWZqhs3NJXUMdPLWsr5k67hPZYuqg4ozLccx0xdLswapj0mn8ovZhK1tKIKiAFAOMO","expires_in":7200,"got_token_at":1467012449}
\ No newline at end of file
+{"access_token":"b_Pc60Dd5eyg_ut3cHbsjQO9EJJdj2Qj5F99o9LH9ltKSme7_FZ3Of22lWLL-K2V0siWzv-bd9PO0Dn-L1PBvIy9LhXa0qPVaFl6vTtZHR2kA8qjo1ps2ancya0t7KmzURGbAFAAXM","expires_in":7200,"got_token_at":1467976842}
\ No newline at end of file
diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
index 5fe7efc51..6bca5753e 100644
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -1046,11 +1046,12 @@ class UsersController < ApplicationController
           homework_detail_group.save if homework_detail_group
 
           if homework.homework_type != 3
-            unless homework.course.nil?
+            students = homework.course.student
+            if !homework.course.nil? && !students.empty?
               name = homework.name
               name_str = name + "的作品提交"
               str = ""
-              homework.course.student.each do |student|
+              students.each do |student|
                 if str != ""
                   str += ","
                 end
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 4ebb8eb80..23fd401fd 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -3282,7 +3282,7 @@ end
 
 def strip_html(text,len=0,endss="...")
   ss = ""
-  if text.length>0
+  if !text.nil? && text.length>0
     ss=text.gsub(/<\/?.*?>/, '').strip
     ss = ss.gsub(/&nbsp;/, ' ')