db: set timestamps to not null.

db/migrate/20191116021759_set_timestamps_to_not_null.rb

@@ -0,0 +1,24 @@
+class SetTimestampsToNotNull < ActiveRecord::Migration[6.0]
+  def change
+    execute "set statement_timeout = 0"
+
+    tables = %i[
+      api_keys artist_commentaries artist_commentary_versions artist_urls
+      artist_versions artists bans bulk_update_requests comment_votes comments
+      delayed_jobs dmail_filters dmails favorite_groups forum_posts
+      forum_topic_visits forum_topics ip_bans janitor_trials mod_actions
+      news_updates notes note_versions pools posts post_appeals post_flags
+      post_votes saved_searches tag_aliases tag_implications uploads
+      user_feedback user_name_change_requests user_password_reset_nonces
+      wiki_pages wiki_page_versions
+    ]
+
+    tables.each do |t|
+      change_column_null t, :created_at, false
+      change_column_null t, :updated_at, false
+    end
+
+    # note: users.updated_at can be null.
+    change_column_null :users, :created_at, false
+  end
+end