课程动态，无对应数据时报错

app/helpers/courses_helper.rb

@@ -682,28 +682,30 @@ module CoursesHelper
     # activity = CourseActivity.first
     title = ""
     url = ""
-    case activity.course_act_type
-      when "Course"
-        title = activity.course_act.name
-        url = course_path activity.course
-      when "HomeworkCommon"
-        title = "作业 " + activity.course_act.name
-        url = student_work_index_path(:homework => activity.course_act.id)
-      when "News"
-        title = "通知公告 " + activity.course_act.title
-        url = course_news_index_path(activity.course)
-      when "Attachment"
-        title = "课件 " + activity.course_act.filename
-        url = course_files_path(activity.course)
-      when "Message"
-        title = "课程讨论区 " + activity.course_act.subject
-        url = course_boards_path(activity.course,:parent_id => activity.course_act.parent_id ? activity.course_act.parent_id : activity.course_act.id, :topic_id => activity.course_act.id)
-      when "JournalsForMessage"
-        title = "留言 " + activity.course_act.notes
-        url = course_feedback_path(activity.course)
-      when "Poll"
-        title = "问卷 " + activity.course_act.polls_name
-        url = poll_index_path(:polls_type => "Course", :polls_group_id => activity.course_id)
+    if activity.course_act
+      case activity.course_act_type
+        when "Course"
+          title = activity.course_act.name
+          url = course_path activity.course
+        when "HomeworkCommon"
+          title = "作业 " + activity.course_act.name
+          url = student_work_index_path(:homework => activity.course_act.id)
+        when "News"
+          title = "通知公告 " + activity.course_act.title
+          url = course_news_index_path(activity.course)
+        when "Attachment"
+          title = "课件 " + activity.course_act.filename
+          url = course_files_path(activity.course)
+        when "Message"
+          title = "课程讨论区 " + activity.course_act.subject
+          url = course_boards_path(activity.course,:parent_id => activity.course_act.parent_id ? activity.course_act.parent_id : activity.course_act.id, :topic_id => activity.course_act.id)
+        when "JournalsForMessage"
+          title = "留言 " + activity.course_act.notes
+          url = course_feedback_path(activity.course)
+        when "Poll"
+          title = "问卷 " + activity.course_act.polls_name
+          url = poll_index_path(:polls_type => "Course", :polls_group_id => activity.course_id)
+      end
     end
     link_to title.gsub(/<(?!img)[^>]*>/,'').html_safe, url, :class => "problem_tit c_dblue fl fb"
   end