You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: 20220810131625_remove_dev_prod_differences.rb
    path of file: ./repos/e621ng/db/migrate
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class RemoveDevProdDifferences < ActiveRecord::Migration[6.1]
  def change
    execute "DROP FUNCTION IF EXI
    
  def change
    execute "DROP FUNCTION IF EXISTS sourcepattern";

    non_null_timestamps(:artist_urls)
    non_null_timestamps(:artists)
    non_null_timestamps(:bans)
    non_null_timestamps(:comments)
    non_null_timestamps(:forum_posts)
    non_null_timestamps(:note_versions)
    non_null_timestamps(:notes)
    non_null_timestamps(:pools)
    non_null_timestamps(:wiki_page_versions)
    non_null_timestamps(:wiki_pages)

    change_column_null :bans, :user_id, false

    change_column_null :forum_topics, :creator_ip_addr, false

    change_column_default :note_versions, :version, nil

    change_column_null :pools, :name, false

    change_column_null :post_versions, :updater_ip_addr, false

    change_column_null :posts, :has_active_children, false
    change_column_null :posts, :created_at, false
    change_column_default :posts, :source, nil

    change_column :tags, :category, :smallint

    change_column_null :post_sets, :description, false

    change_column_default :users, :per_page, 75
    change_column_default :users, :comment_threshold, -2

    change_column_null :post_flags, :created_at, false
  end