commentary versions: migrate columns to non-null.

Fixes #4355.

db/migrate/20200325073456_change_fields_to_non_null_on_artist_commentary_versions.rb

@@ -0,0 +1,25 @@
+class ChangeFieldsToNonNullOnArtistCommentaryVersions < ActiveRecord::Migration[6.0]
+  def up
+    change_column_null(:artist_commentary_versions, :original_title, false, "")
+    change_column_null(:artist_commentary_versions, :translated_title, false, "")
+    change_column_null(:artist_commentary_versions, :original_description, false, "")
+    change_column_null(:artist_commentary_versions, :translated_description, false, "")
+
+    change_column_default(:artist_commentary_versions, :original_title, "")
+    change_column_default(:artist_commentary_versions, :translated_title, "")
+    change_column_default(:artist_commentary_versions, :original_description, "")
+    change_column_default(:artist_commentary_versions, :translated_description, "")
+  end
+
+  def down
+    change_column_null(:artist_commentary_versions, :original_title, true)
+    change_column_null(:artist_commentary_versions, :translated_title, true)
+    change_column_null(:artist_commentary_versions, :original_description, true)
+    change_column_null(:artist_commentary_versions, :translated_description, true)
+
+    change_column_default(:artist_commentary_versions, :original_title, nil)
+    change_column_default(:artist_commentary_versions, :translated_title, nil)
+    change_column_default(:artist_commentary_versions, :original_description, nil)
+    change_column_default(:artist_commentary_versions, :translated_description, nil)
+  end
+end

db/structure.sql

@@ -486,10 +486,10 @@ CREATE TABLE public.artist_commentary_versions (
     post_id integer NOT NULL,
     updater_id integer NOT NULL,
     updater_ip_addr inet NOT NULL,
-    original_title text,
+    original_title text DEFAULT ''::text NOT NULL,
-    original_description text,
+    original_description text DEFAULT ''::text NOT NULL,
-    translated_title text,
+    translated_title text DEFAULT ''::text NOT NULL,
-    translated_description text,
+    translated_description text DEFAULT ''::text NOT NULL,
     created_at timestamp without time zone NOT NULL,
     updated_at timestamp without time zone NOT NULL
 );
@@ -7370,6 +7370,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20200307021204'),
 ('20200309035334'),
 ('20200309043653'),
-('20200318224633');
+('20200318224633'),
+('20200325073456');