If an attribute has an enumeration type it is supposed to silently fail if we pass a value that's not in the enum. However, we should allow null in the case of a nullable attribute.
<rdar://problem/113591277>
Pull request: https://github.com/WebKit/WebKit/pull/16495
Committed 266726@main (23551a03b824): <https://commits.webkit.org/266726@main> Reviewed commits have been landed. Closing PR #16495 and removing active labels.