diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 738a56985..fcd512750 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.26.21",
+    "version": "2.26.22",
     "bin": "bin/hydrooj.js",
     "main": "dist/loader.js",
     "typings": "dist/loader.d.ts",
diff --git a/packages/hydrooj/src/handler/contest.ts b/packages/hydrooj/src/handler/contest.ts
index cf3557a32..073f1882a 100644
--- a/packages/hydrooj/src/handler/contest.ts
+++ b/packages/hydrooj/src/handler/contest.ts
@@ -214,7 +214,7 @@ class ContestEditHandler extends Handler {
         domainId: string, beginAtDate: string, beginAtTime: string, duration: number,
         title: string, content: string, rule: string, _pids: string, rated = false,
     ) {
-        const pids = _pids.replace(/，/g, ',').split(',').map((i) => +i);
+        const pids = _pids.replace(/，/g, ',').split(',').map((i) => +i).filter((i) => i);
         await problem.getList(domainId, pids, this.user.hasPerm(PERM.PERM_VIEW_PROBLEM_HIDDEN), true);
         const beginAtMoment = moment.tz(`${beginAtDate} ${beginAtTime}`, this.user.timeZone);
         if (!beginAtMoment.isValid()) {
@@ -425,7 +425,7 @@ class ContestCreateHandler extends Handler {
         domainId: string, beginAtDate: string, beginAtTime: string, duration: number,
         title: string, content: string, rule: string, _pids: string, rated = false,
     ) {
-        const pids = _pids.replace(/，/g, ',').split(',').map((i) => +i);
+        const pids = _pids.replace(/，/g, ',').split(',').map((i) => +i).filter((i) => i);
         const beginAt = moment.tz(`${beginAtDate} ${beginAtTime}`, this.user.timeZone);
         if (!beginAt.isValid()) throw new ValidationError('beginAtDate', 'beginAtTime');
         const endAt = beginAt.clone().add(duration, 'hours').toDate();
diff --git a/packages/hydrooj/src/handler/homework.ts b/packages/hydrooj/src/handler/homework.ts
index 8a0ac9348..f61cad357 100644
--- a/packages/hydrooj/src/handler/homework.ts
+++ b/packages/hydrooj/src/handler/homework.ts
@@ -259,7 +259,7 @@ class HomeworkCreateHandler extends Handler {
         penaltySinceDate: string, penaltySinceTime: string, extensionDays: number,
         penaltyRules: PenaltyRules, title: string, content: string, _pids: string, rated = false,
     ) {
-        const pids = _pids.replace(/，/g, ',').split(',').map((i) => +i);
+        const pids = _pids.replace(/，/g, ',').split(',').map((i) => +i).filter((i) => i);
         const beginAt = moment.tz(`${beginAtDate} ${beginAtTime}`, this.user.timeZone);
         if (!beginAt.isValid()) throw new ValidationError('beginAtDate', 'beginAtTime');
         const penaltySince = moment.tz(`${penaltySinceDate} ${penaltySinceTime}`, this.user.timeZone);
@@ -323,7 +323,7 @@ class HomeworkEditHandler extends Handler {
         penaltySinceDate: string, penaltySinceTime: string, extensionDays: number,
         penaltyRules: string, title: string, content: string, _pids: string, rated = false,
     ) {
-        const pids = _pids.replace(/，/g, ',').split(',').map((i) => +i);
+        const pids = _pids.replace(/，/g, ',').split(',').map((i) => +i).filter((i) => i);
         const tdoc = await contest.get(domainId, tid, document.TYPE_HOMEWORK);
         if (!this.user.own(tdoc)) this.checkPerm(PERM.PERM_EDIT_HOMEWORK);
         else this.checkPerm(PERM.PERM_EDIT_HOMEWORK_SELF);
diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index 2be141491..40e527c7e 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -629,6 +629,10 @@ export class ProblemPrefixListHandler extends Handler {
     @param('prefix', Types.Name)
     async get(domainId: string, prefix: string) {
         this.response.body = await problem.getPrefixList(domainId, prefix);
+        if (!Number.isNaN(+prefix)) {
+            const pdoc = await problem.get(domainId, +prefix, undefined, ['domainId', 'docId', 'pid', 'title']);
+            if (pdoc) this.response.body.unshift(pdoc);
+        }
     }
 }