UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36

Steps to reproduce the problem:
1. Go to https://w3c.github.io/uievents/tools/key-event-viewer.html
2. Press key which is NOT supported by the OS.

What is the expected behavior?
The code value should be "Unidentified".

What went wrong?
Perhaps, it becomes null or empty string.

Did this work before? No 

Does this work in other browsers? No
 I'm still not sure how to reproduce this actually though, but as far as I read the source code of Chromium, there is this bug.

Chrome version: 65.0.3325.181  Channel: n/a
OS Version: 10.0
Flash Version: 

Older draft of UI Events code value, when code value cannot be resolved, it should've been empty string.  However, newer drafts declare "Unidentified" should be set.
https://w3c.github.io/uievents-code/#code-Unidentified

I'm trying to update some KeyboardEvent.code values of Firefox from legacy values to the latest values. However, I'm still afraid to use "Unidentified" since Chromium still uses null or empty string.

A lot of "Code" is mapped to NULL here:
https://cs.chromium.org/chromium/src/ui/events/keycodes/dom/keycode_converter_data.inc

And NULL mapped to empty string here:
https://cs.chromium.org/chromium/src/ui/events/keycodes/dom/keycode_converter.cc?l=120&rcl=81f17cb2241ab29dc07cc55f83e715ce2606fa0a