课程动态报错

app/helpers/courses_helper.rb

@@ -711,6 +711,7 @@ module CoursesHelper
   #课程动态的描述
   def course_activity_desc activity
     desc = ""
+    if activity.course_act
       case activity.course_act_type
         when "Course"
           desc = ""
@@ -727,6 +728,7 @@ module CoursesHelper
         when "Poll"
           desc = activity.course_act.polls_description
       end
+    end
     desc.html_safe
   end
 end