Description

Version: jQuery 3.4.1

Since 0ba8e38 it appears that using contents() to get the children of an <object> is not working as expected.

Taking this example HTML

<object type="application/x-shockwave-flash" width="200" height="300" id="penguin">
    <param name="movie" value="flash/penguin.swf">
    <param name="quality" value="high">
    <img src="images/penguin.jpg" width="200" height="300" alt="Penguin">
</object>

I'd expect the following to happen

jQuery(objectHtml).contents().length // => 3

But what actually happens is:

jQuery(objectHtml).contents().length // => 0

This happens because on this line

If we change the conditional to be elem.contentDocument != null it works correctly.

Link to test case

https://codepen.io/patocallaghan/pen/bybaWv?editors=0011

I have a PR to fix it but I wanted to open an issue first.