fix: closes #11511

reset all user skins if they are no longer available

src/upgrades/3.1.0/reset_user_bootswatch_skin.js

@@ -0,0 +1,24 @@
+'use strict';
+
+
+const db = require('../../database');
+
+module.exports = {
+	name: 'Reset old bootswatch skin for all users',
+	timestamp: Date.UTC(2023, 4, 1),
+	method: async function () {
+		const batch = require('../../batch');
+		const css = require('../../meta/css');
+
+		batch.processSortedSet('users:joindate', async (uids) => {
+			let settings = await db.getObjects(uids.map(uid => `user:${uid}:settings`));
+			settings = settings.filter(
+				s => s && s.bootswatchSkin && !css.supportedSkins.includes(s.bootswatchSkin)
+			);
+
+			await db.setObjectBulk(settings.map(s => ([`user:${s.uid}`, { bootswatchSkin: '' }])));
+		}, {
+			batch: 500,
+		});
+	},
+};