Description

In jQuery 3.6.0,$element.css("--custom") correctly returnedundefined for a custom property that isn’t set. But in jQuery 3.6.1, it crashes withTypeError: ret is undefined.

This breaks the Zulip settings dialog.

This was presumably introduced by#4930 (cc@fecore1@mgol).

Link to test case

https://codepen.io/anderskaseorg/pen/rNvNZWW