fix(用例管理): 修复用例评论无法回复问题

--bug=1035920 --user=郭雨琦 https://www.tapd.cn/55049933/bugtrace/bugs/view/1155049933001035920

backend/services/case-management/src/main/java/io/metersphere/functional/service/FunctionalCaseCommentService.java

@@ -277,7 +277,11 @@ public class FunctionalCaseCommentService {
         Map<String, List<FunctionalCaseCommentDTO>> commentMap = replyList.stream().collect(Collectors.groupingBy(FunctionalCaseComment::getParentId));
         for (FunctionalCaseCommentDTO functionalCaseComment : rootList) {
             List<FunctionalCaseCommentDTO> replyComments = commentMap.get(functionalCaseComment.getId());
+            if (CollectionUtils.isNotEmpty(replyComments)) {
                 functionalCaseComment.setChildComments(replyComments);
+            } else {
+                functionalCaseComment.setChildComments(new ArrayList<>());
+            }
         }
         return rootList;
     }