Which package(s) are affected?

Lit Core (lit / lit-html / lit-element / reactive-element)

Description

❓ is the ref directive supposed to accept an undefined for argument?
Looks like that yes based on the exported types (that are derived from here
However, both the disconnected & reconnected lifecyles are doing unsafe usage of the ref.

I'll be glad to bring a fix upstream for that 🙂
However, I see two possible fixes, and I'd like to see which one we want to go with:
Either we consider the issue to be the looseness of the argument, and restrict it from RefCallback|undefined to RefCallback
Or, we go the opposite way and we ensure the internal _ref property is used safely.****

Reproduction

https://lit.dev/playground/#sample=examples%2Fhello-world&gist=0b002ac6df87f09ff2344481e719cce4

1. Open DevTools
2. Check the console
3. It throw a runtime error

Workaround

Marshall value prior to using the directive, <div ${arg ? ref(arg) : nothing}></div>

Is this a regression?

No or unsure. This never worked, or I haven't tried before.

Affected versions

3.3.1

Browser/OS/Node environment

Browser: Chrome 144.0.7559.97
OS: macOS 26.2 (25C56)