Corrected migration, to populate the new tags table

db/migrate/20161210154558_populate_tags.rb

@@ -1,14 +1,14 @@
 # Migrate tags from inline attribute to separate table
 class PopulateTags < ActiveRecord::Migration
   def self.up
+    change_column_null :events, :tags, true
+    change_column_null :orgas, :tags, true
+
     execute('SELECT id, tags FROM events;').each do |result|
       event = Event.find_by id: result[0]
       event.tag_list = result[1]
       event.save
     end
-
-    change_column_null :events, :tags, true
-    change_column_null :orgas, :tags, true
   end
 
   def self.down