diff --git a/modules/user.js b/modules/user.js
index 508bc94..5a30c43 100644
--- a/modules/user.js
+++ b/modules/user.js
@@ -87,6 +87,7 @@ app.get('/user/:id', async (req, res) => {
   try {
     let id = parseInt(req.params.id);
     let user = await User.fromID(id);
+    if (!user) throw new ErrorMessage('无此用户。');
     user.ac_problems = await user.getACProblems();
     user.articles = await user.getArticles();
     user.allowedEdit = await user.isAllowedEditBy(res.locals.user);
@@ -138,6 +139,7 @@ app.post('/user/:id/edit', async (req, res) => {
   try {
     let id = parseInt(req.params.id);
     user = await User.fromID(id);
+    if (!user) throw new ErrorMessage('无此用户。');
 
     let allowedEdit = await user.isAllowedEditBy(res.locals.user);
     if (!allowedEdit) throw new ErrorMessage('您没有权限进行此操作。');
diff --git a/views/header.ejs b/views/header.ejs
index 3fad227..f51502d 100644
--- a/views/header.ejs
+++ b/views/header.ejs
@@ -1,6 +1,6 @@
 <% include util %>
 <!DOCTYPE html>
-<html>
+<html lang="zh-CN">
 <head>
     <meta charset="utf-8">
     <meta content="IE=edge" http-equiv="X-UA-Compatible">
diff --git a/views/problem.ejs b/views/problem.ejs
index ef5a84b..50f8c08 100644
--- a/views/problem.ejs
+++ b/views/problem.ejs
@@ -242,6 +242,7 @@ if (contest) {
   <script src="/libs/ace/ace.js"></script>
   <script type="text/javascript">
   var editor = ace.edit("editor");
+  var lastSubmitted = '';
 
   editor.setTheme("ace/theme/tomorrow");
   editor.getSession().setMode("ace/mode/" + $('#languages-menu .item.active').data('mode'));
@@ -256,6 +257,7 @@ if (contest) {
   function submit_code() {
     if (!editor.getValue().trim()) return false;
     $('#submit_code input[name=language]').val($('#languages-menu .item.active').data('value'));
+    lastSubmitted = editor.getValue();
     $('#submit_code input[name=code]').val(editor.getValue());
     return true;
   }
