判断org.org_act_id是否为空

app/views/organizations/_org_activities.html.erb

@@ -50,7 +50,7 @@
             <% end %>
         <% end %>
         <% if act.container_type == 'OrgSubfield' %>
-            <% if act.org_act_type == 'Message' %>
+            <% if act.org_act_type == 'Message' and act.org_act_id %>
                 <% message = Message.find(act.org_act_id) %>
                 <% if !message.board.course_id.nil? %>
                     <%= render :partial => 'org_course_message', :locals => {:activity => message,:user_activity_id =>act.id} %>