Deprecation notice on lesson report

[donnapep]

Steps to Reproduce

1. Enable define( 'WP_DEBUG_DISPLAY', true ); in wp-config.php.
2. Go to the Students taking this Lesson report (wp-admin/admin.php?page=sensei_reports&lesson_id=<lesson_id>).
3. See deprecation notice*.
4. Export the rows.

*Note that this only happened for some lessons; other lessons were fine. I noticed that I only saw the deprecation message when more than 2 students had taken the lesson, but the cause could be something else. So this may take a bit of digging / testing different scenarios. See screenshots below.

What I Expected

No deprecation notice and the rows to export without issue.

What Happened Instead

The following deprecation notice is displayed:

PHP Deprecated:  preg_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in /Users/donnapep/Local Sites/senseitheme/app/public/wp-includes/kses.php on line 1805

The export looks like this:

Screenshots

[merkushin]

@m1r0 addressed this issue in #7644

Can't reproduce it anymore.