Description

When using Joomla’s versioning system to compare two versions of an item that includes subform fields, the following error is thrown:

htmlspecialchars(): Argument #1 ($string) must be of type string, stdClass given

This occurs when subform field values are stored as an object (stdClass) and Joomla attempts to render them as if they were simple strings.

Steps to Reproduce

1. Enable Content Versioning in Joomla.
2. Create an article (or any item in a component) that has a Subform field.
3. Save the item → Version 1 created.
4. Edit the item, change subform values, and save again → Version 2 created.
5. Open Versions and try to Compare Version 1 and Version 2.
   Here is the video link to reproduce the issue
   https://sc.com.ly/show/eeda3d41-9dd1-4bb9-9f27-758072633787

Expected Result

Joomla should highlight the specific changes in subform values without throwing an error.

Actual Result

The system throws the following error:

htmlspecialchars(): Argument #1 ($string) must be of type string, stdClass given

Additional Notes

• This affects both Joomla core (com_content with subform fields) and custom components generated by Component Creator.
• Joomla version: [insert version tested, e.g., 5.1.x or 4.x].
• PHP version: [insert version].