core: optional files

packages/hydrooj/package.json

@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "3.1.12",
+    "version": "3.1.13",
     "bin": "bin/hydrooj.js",
     "main": "src/loader",
     "module": "src/loader",

packages/hydrooj/src/handler/problem.ts

@@ -480,9 +480,9 @@ export class ProblemFilesHandler extends ProblemDetailHandler {
         const links = {};
         const size = Math.sum(
             this.pdoc[type === 'testdata' ? 'data' : 'additional_file']
-                .filter((i) => files.has(i.name))
-                .map((i) => i.size),
-        );
+                ?.filter((i) => files.has(i.name))
+                ?.map((i) => i.size),
+        ) || 0;
         await oplog.add({
             type: 'bulkDownload',
             time: new Date(),