大题描述bugfix

src/features/examwork/StudentExamDetail/PreviewPaperDialog.vue

@@ -351,6 +351,7 @@ export default {
       return contents;
     },
     parseTopicDesc(richJson) {
+      if (!richJson) return [];
       const bodys = this.transformRichJson(richJson);
       return bodys.map((body) => {
         return {