fix: guard against a null comment when updating it - EXO-88900

SonarCloud reported a possible NullPointerException (javabugs:S2259) on the
update endpoint: CommentStorageImpl.updateComment() returns the result of
StorageUtil.commentToDto(), which is null when the DAO update returns null,
and the endpoint dereferenced it right away. Since the refactoring, the
endpoint no longer loads the comment beforehand, which made that path
reachable.

The endpoint now answers a server error instead of failing with a NPE, and
the case is covered by a test.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Julien-Dubois-eXo

services/src/main/java/org/exoplatform/task/rest/TaskRestService.java

@@ -1098,6 +1098,10 @@ public Response updateComment(@Parameter(description = "Comment text", required
     commentText = commentText.replace("+", "%2b");
     commentText = URLDecoder.decode(commentText, "UTF-8");
     CommentDto updatedComment = commentService.updateComment(commentId, commentText, currentUserIdentity);
+    if (updatedComment == null) {
+      LOG.error("Comment {} could not be updated", commentId);
+      return Response.serverError().build();
+    }
     transformHtml(updatedComment, currentUserIdentity);
     CommentEntity commentEntity = new CommentEntity(updatedComment,
                                                     userService.loadUser(updatedComment.getAuthor()),

services/src/test/java/org/exoplatform/task/rest/TestTaskRestService.java

@@ -904,6 +904,11 @@ public void testUpdateComment() throws Exception {
                                      any())).thenThrow(new RuntimeException("Unexpected error"));
     response = taskRestService.updateComment("brokenText", 1);
     assertEquals(Response.Status.INTERNAL_SERVER_ERROR.getStatusCode(), response.getStatus());
+
+    // The service returns no comment at all
+    when(commentService.updateComment(eq(1L), eq("noResultText"), any())).thenReturn(null);
+    response = taskRestService.updateComment("noResultText", 1);
+    assertEquals(Response.Status.INTERNAL_SERVER_ERROR.getStatusCode(), response.getStatus());
   }
 
   @Test