From 08148832bd7e27938d7b80ab8210f510162d10cc Mon Sep 17 00:00:00 2001
From: Jonathan Bredo <Bredo@users.noreply.github.com>
Date: Wed, 1 Jul 2026 03:45:18 +0200
Subject: [PATCH] Enhance serialization with optional chaining and checks

Added optional chaining to safely check for class presence and attribute setting. Improved handling of nesting level attribute assignment.
---
 .../exporters/html/util/serializeBlocksExternalHTML.ts    | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts b/packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts
index 064a9af6b5..a3245fa5ba 100644
--- a/packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts
+++ b/packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts
@@ -227,7 +227,8 @@ function serializeBlock<
 
   const elementFragment = doc.createDocumentFragment();
 
-  if ((ret.dom as HTMLElement).classList.contains("bn-block-content")) {
+  // Needs optional chaining for handling <ol> lists export
+  if ((ret.dom as HTMLElement).classList?.contains("bn-block-content")) {
     const blockContentDataAttributes = [
       ...attrs,
       ...Array.from((ret.dom as HTMLElement).attributes),
@@ -242,13 +243,12 @@ function serializeBlock<
         attr.name !== "data-editable",
     );
 
-    // ret.dom = ret.dom.firstChild! as any;
     for (const attr of blockContentDataAttributes) {
       (ret.dom.firstChild! as HTMLElement).setAttribute(attr.name, attr.value);
     }
 
     addAttributesAndRemoveClasses(ret.dom.firstChild! as HTMLElement);
-    if (nestingLevel > 0) {
+    if (nestingLevel > 0 && typeof (ret.dom.firstChild as HTMLElement)?.setAttribute === 'function') {
       (ret.dom.firstChild! as HTMLElement).setAttribute(
         "data-nesting-level",
         nestingLevel.toString(),
@@ -257,7 +257,7 @@ function serializeBlock<
     elementFragment.append(...Array.from(ret.dom.childNodes));
   } else {
     elementFragment.append(ret.dom);
-    if (nestingLevel > 0) {
+    if (nestingLevel > 0 && typeof (ret.dom as HTMLElement).setAttribute === 'function') {
       (ret.dom as HTMLElement).setAttribute(
         "data-nesting-level",
         nestingLevel.toString(),