Fix #3480: NoMethodError error when adding artist tag to post.

script/fixes/052_fix_tag_timestamps.rb

@@ -0,0 +1,16 @@
+#!/usr/bin/env ruby
+
+require File.expand_path(File.join(File.dirname(__FILE__), '..', '..', 'config', 'environment'))
+
+CurrentUser.user = User.system
+CurrentUser.ip_addr = "127.0.0.1"
+
+Tag.transaction do
+  Tag.without_timeout do
+    puts "Tag.where(updated_at: nil).count = #{Tag.where(updated_at: nil).count}"
+    puts "Tag.where(created_at: nil).count = #{Tag.where(created_at: nil).count}"
+
+    Tag.where(updated_at: nil).update_all(updated_at: Time.zone.now)
+    Tag.where(created_at: nil).update_all("created_at = updated_at")
+  end
+end