In case $content is null, we should not add it to _style array. I would early return in this case. So add the lines of code below to beginning of the method to prevent warning:

if ($content === null) {
	return $this;
}

In the future (not sure if Joomla 5 is suitable), we should use string type for $content parameter so that we do not have to add ugly code like that.

Updated, thank you @joomdonation

I think I fixed the code style but the build was killed somehow?

I restarted it.

Thank you! Looks like it's good now.

I have tested this item ✅ successfully on 9914810

Code review.

This pull request has been automatically rebased to 4.3-dev.

We need just one more test, this is tiny. Can someone review it so it can be merged into the next release?

@crystalenka When you do a branch update, test counter in the issue tracker is reset, so you have to add back the test result with use of the issue tracker (button "Alter test"). Otherwise nobody will find it when filtering by "Has 2 test" or "Needs 1 test". I will do that for you now, but in future please avoid unnecessary branch updates.

Ah I just see the PR has been rebased, so it needs new tests anyway.

@richard67 it has been rebased, but it's a very minor change (just ~3 lines of code). Hopefully it can be tested and merged soon. ?

We tested this fix in a 4.3.3 / PHP 8.1.21 build, the issue is actually on line 649 of Document.php for this build, and it looks great. FWIW

Thanks Crystal @crystalenka for the PR!