diff --git a/src/main/java/run/halo/app/controller/admin/api/RecoveryController.java b/src/main/java/run/halo/app/controller/admin/api/RecoveryController.java
index c425d4f41..228f8fd61 100644
--- a/src/main/java/run/halo/app/controller/admin/api/RecoveryController.java
+++ b/src/main/java/run/halo/app/controller/admin/api/RecoveryController.java
@@ -7,6 +7,7 @@ import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestPart;
 import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.multipart.MultipartFile;
+import run.halo.app.cache.lock.CacheLock;
 import run.halo.app.exception.BadRequestException;
 import run.halo.app.model.properties.PrimaryProperties;
 import run.halo.app.service.OptionService;
@@ -34,6 +35,7 @@ public class RecoveryController {
 
     @PostMapping("migrations/v0_4_3")
     @ApiOperation("Migrates from halo v0.4.3")
+    @CacheLock
     public void migrateFromVersion_0_4_3(
             @ApiParam("This file content type should be json")
             @RequestPart("file") MultipartFile file) {
diff --git a/src/main/java/run/halo/app/service/base/BaseCommentService.java b/src/main/java/run/halo/app/service/base/BaseCommentService.java
index 7ea29e89b..6c53b6db2 100644
--- a/src/main/java/run/halo/app/service/base/BaseCommentService.java
+++ b/src/main/java/run/halo/app/service/base/BaseCommentService.java
@@ -29,6 +29,7 @@ public interface BaseCommentService<COMMENT extends BaseComment> extends CrudSer
      * %s: parent commentator author name
      * %s: comment content
      */
+    @Deprecated
     String COMMENT_TEMPLATE = "<a href='#comment-id-%d'>@%s</a> %s";
 
     /**
@@ -157,7 +158,7 @@ public interface BaseCommentService<COMMENT extends BaseComment> extends CrudSer
     /**
      * Target must exist.
      *
-     * @param targetId target id must not be null
+     * @param targetId target id must not be null (post id, sheet id or journal id)
      */
     void targetMustExist(@NonNull Integer targetId);
 }
diff --git a/src/main/java/run/halo/app/service/impl/BaseCommentServiceImpl.java b/src/main/java/run/halo/app/service/impl/BaseCommentServiceImpl.java
index ef23dad65..4c079cbbc 100644
--- a/src/main/java/run/halo/app/service/impl/BaseCommentServiceImpl.java
+++ b/src/main/java/run/halo/app/service/impl/BaseCommentServiceImpl.java
@@ -105,17 +105,10 @@ public abstract class BaseCommentServiceImpl<COMMENT extends BaseComment> extend
         // List all the top comments (Caution: This list will be cleared)
         List<COMMENT> comments = baseCommentRepository.findAllByPostIdAndStatus(postId, CommentStatus.PUBLISHED);
 
-        // Init the top virtual comment
-        BaseCommentVO topVirtualComment = new BaseCommentVO();
-        topVirtualComment.setId(0L);
-        topVirtualComment.setChildren(new LinkedList<>());
-
         Comparator<BaseCommentVO> commentVOComparator = buildCommentComparator(pageable.getSortOr(Sort.by(Sort.Direction.DESC, "createTime")));
 
-        // Concrete the comment tree
-        concreteTree(topVirtualComment, new LinkedList<>(comments), commentVOComparator);
-
-        List<BaseCommentVO> topComments = topVirtualComment.getChildren();
+        // Convert to vo
+        List<BaseCommentVO> topComments = convertToVo(comments, commentVOComparator);
 
         List<BaseCommentVO> pageContent;
 
@@ -370,6 +363,30 @@ public abstract class BaseCommentServiceImpl<COMMENT extends BaseComment> extend
         };
     }
 
+    /**
+     * Converts to base comment vo tree.
+     *
+     * @param comments   comments list could be null
+     * @param comparator comment comparator could be null
+     * @return a comment vo tree
+     */
+    @NonNull
+    protected List<BaseCommentVO> convertToVo(@Nullable List<COMMENT> comments, @Nullable Comparator<BaseCommentVO> comparator) {
+        if (CollectionUtils.isEmpty(comments)) {
+            return Collections.emptyList();
+        }
+
+        // Init the top virtual comment
+        BaseCommentVO topVirtualComment = new BaseCommentVO();
+        topVirtualComment.setId(0L);
+        topVirtualComment.setChildren(new LinkedList<>());
+
+        // Concrete the comment tree
+        concreteTree(topVirtualComment, new LinkedList<>(comments), comparator);
+
+        return topVirtualComment.getChildren();
+    }
+
     /**
      * Concretes comment tree.
      *
@@ -379,9 +396,8 @@ public abstract class BaseCommentServiceImpl<COMMENT extends BaseComment> extend
      */
     protected void concreteTree(@NonNull BaseCommentVO parentComment,
                                 @Nullable Collection<COMMENT> comments,
-                                @NonNull Comparator<BaseCommentVO> commentComparator) {
+                                @Nullable Comparator<BaseCommentVO> commentComparator) {
         Assert.notNull(parentComment, "Parent comment must not be null");
-        Assert.notNull(commentComparator, "Comment comparator must not be null");
 
         if (CollectionUtils.isEmpty(comments)) {
             return;
@@ -419,7 +435,9 @@ public abstract class BaseCommentServiceImpl<COMMENT extends BaseComment> extend
             // Recursively concrete the children
             parentComment.getChildren().forEach(childComment -> concreteTree(childComment, comments, commentComparator));
             // Sort the children
-            parentComment.getChildren().sort(commentComparator);
+            if (commentComparator != null) {
+                parentComment.getChildren().sort(commentComparator);
+            }
         }
     }