Do nothing if no created_at in dojos.yaml

Author: yasulab

lib/tasks/dojos.rake

@@ -36,7 +36,7 @@ namespace :dojos do
       d.logo        = dojo['logo']
       d.tags        = dojo['tags']
       d.url         = dojo['url']
-      d.created_at  = d.new_record? ? Time.zone.now : dojo['created_at']
+      d.created_at  = d.new_record? ? Time.zone.now : dojo['created_at'] || d.created_at
       d.updated_at  = Time.zone.now
       d.prefecture_id = dojo['prefecture_id']