From eb4288219ecb38ec4e38f32588089dec07d8f312 Mon Sep 17 00:00:00 2001
From: Aaron Dodson <adodson@google.com>
Date: Tue, 13 Jan 2026 14:52:19 -0800
Subject: [PATCH] fix: Fix bug that prevented redoing adding empty block
 comments (#9568)

* fix: Fix bug that prevented redoing adding empty block comments

* test: Add tests for undoing/redoing adding comments

* test: Add tests for un/redoing adding non-empty comments
---
 core/events/events_block_change.ts |  2 +-
 tests/mocha/comment_test.js        | 45 ++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/core/events/events_block_change.ts b/core/events/events_block_change.ts
index e71eabb17..d4a8ba9d2 100644
--- a/core/events/events_block_change.ts
+++ b/core/events/events_block_change.ts
@@ -193,7 +193,7 @@ export class BlockChange extends BlockBase {
         break;
       }
       case 'comment':
-        block.setCommentText((value as string) || null);
+        block.setCommentText((value as string) ?? null);
         break;
       case 'collapsed':
         block.setCollapsed(!!value);
diff --git a/tests/mocha/comment_test.js b/tests/mocha/comment_test.js
index 1f52df8fd..a7b2635b9 100644
--- a/tests/mocha/comment_test.js
+++ b/tests/mocha/comment_test.js
@@ -167,4 +167,49 @@ suite('Comments', function () {
       assertBubbleLocation(this.comment, 100, 100);
     });
   });
+  suite('Undo/Redo', function () {
+    test('Adding an empty comment can be undone', function () {
+      const block = this.workspace.newBlock('empty_block');
+      block.setCommentText('');
+      assert.isNotNull(block.getIcon(Blockly.icons.IconType.COMMENT));
+      assert.equal(block.getCommentText(), '');
+
+      this.workspace.undo(false);
+
+      assert.isUndefined(block.getIcon(Blockly.icons.IconType.COMMENT));
+      assert.isNull(block.getCommentText());
+    });
+
+    test('Adding an empty comment can be redone', function () {
+      const block = this.workspace.newBlock('empty_block');
+      block.setCommentText('');
+      this.workspace.undo(false);
+      this.workspace.undo(true);
+
+      assert.isNotNull(block.getIcon(Blockly.icons.IconType.COMMENT));
+      assert.equal(block.getCommentText(), '');
+    });
+
+    test('Adding a non-empty comment can be undone', function () {
+      const block = this.workspace.newBlock('empty_block');
+      block.setCommentText('hey there');
+      assert.isNotNull(block.getIcon(Blockly.icons.IconType.COMMENT));
+      assert.equal(block.getCommentText(), 'hey there');
+
+      this.workspace.undo(false);
+
+      assert.isUndefined(block.getIcon(Blockly.icons.IconType.COMMENT));
+      assert.isNull(block.getCommentText());
+    });
+
+    test('Adding a non-empty comment can be redone', function () {
+      const block = this.workspace.newBlock('empty_block');
+      block.setCommentText('hey there');
+      this.workspace.undo(false);
+      this.workspace.undo(true);
+
+      assert.isNotNull(block.getIcon(Blockly.icons.IconType.COMMENT));
+      assert.equal(block.getCommentText(), 'hey there');
+    });
+  });
 });