[MM-43500] Fix MattermostAppID null values with NOT NULL constraint (#20028)

db/migrations/postgres/000082_upgrade_oauth_mattermost_app_id.down.sql

@@ -0,0 +1,13 @@
+DO $$
+DECLARE
+    column_exist boolean := false;
+BEGIN
+SELECT count(*) != 0 INTO column_exist
+    FROM information_schema.columns
+    WHERE table_name = 'oauthapps'
+    AND column_name = 'mattermostappid';
+IF column_exist THEN
+    ALTER TABLE OAuthApps ALTER COLUMN MattermostAppID DROP NOT NULL;
+    ALTER TABLE OAuthApps ALTER COLUMN MattermostAppID DROP DEFAULT;
+END IF;
+END $$;

db/migrations/postgres/000082_upgrade_oauth_mattermost_app_id.up.sql

@@ -0,0 +1,14 @@
+DO $$
+DECLARE
+    column_exist boolean := false;
+BEGIN
+SELECT count(*) != 0 INTO column_exist
+    FROM information_schema.columns
+    WHERE table_name = 'oauthapps'
+    AND column_name = 'mattermostappid';
+IF column_exist THEN
+    UPDATE OAuthApps SET MattermostAppID = '' WHERE MattermostAppID IS NULL;
+    ALTER TABLE OAuthApps ALTER COLUMN MattermostAppID SET DEFAULT '';
+    ALTER TABLE OAuthApps ALTER COLUMN MattermostAppID SET NOT NULL;
+END IF;
+END $$;