Fix bug.

app/controllers/announcements_controller.rb

@@ -604,7 +604,7 @@ class AnnouncementsController < ApplicationController
         "title" => announcement.title,
         "subtitle_ann" => subtitle_ann,
         "update_user" => update_user,
-        "updated_at" => announcement.postdate.in_time_zone(Time.zone.utc_offset / 3600).strftime('%Y-%m-%d %H:%M'),
+        "updated_at" => (announcement.postdate.in_time_zone(Time.zone.utc_offset / 3600).strftime('%Y-%m-%d %H:%M') rescue ""),
         "body" =>announcement.text,
         "image" => announcement.image.url,
         "img_src" => img_src,