When interpolating during animation between two empty transform lists ("transform: none" to "transform: none"), the resulting value should be "transform: none". This is covered by failing subtests in imported/w3c/web-platform-tests/css/css-transforms/animation/list-interpolation.html.
Created attachment 448849 [details] Patch
Looks like this also fixed a test within imported/w3c/web-platform-tests/web-animations/interfaces/Animation/commitStyles.html and you'll need to rebase the results.
Created attachment 448911 [details] Patch
Committed r287917 (245950@main): <https://commits.webkit.org/245950@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 448911 [details].
<rdar://problem/87448400>