CSSStyleDeclaration.getPropertyPriority() should return the empty string for invalid CSS properties, not null: https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-getpropertyvalue
Created attachment 431970 [details] Patch
Comment on attachment 431970 [details] Patch r=me
Committed r279125 (239040@main): <https://commits.webkit.org/239040@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 431970 [details].
<rdar://problem/79622278>
Reopening to attach new patch.
Created attachment 432072 [details] Improved test coverage
Committed r279176 (239072@main): <https://commits.webkit.org/239072@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 432072 [details].