ui: optional ul element after select input

packages/ui-default/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@hydrooj/ui-default",
-  "version": "4.38.1",
+  "version": "4.38.2",
   "author": "undefined <i@undefined.moe>",
   "license": "AGPL-3.0",
   "main": "hydro.js",

packages/ui-default/pages/problem_detail.page.jsx

@@ -195,7 +195,7 @@ const page = new NamedPage(['problem_detail', 'contest_detail_problem', 'homewor
             </div>
           `));
         } else {
-          if ($(e).next()[0].tagName !== 'UL') {
+          if ($(e).next()[0]?.tagName !== 'UL') {
             cnt--;
             return;
           }