CSSStyleValue.parse() / CSSStyleValue.parseAll() should throw when passed an empty string as custom property value.
This matches Blink's behavior and this behavior is covered by WPT tests.
Pull request: https://github.com/WebKit/WebKit/pull/5775
Committed 256011@main (98e13fd6a1c2): <https://commits.webkit.org/256011@main>
Reviewed commits have been landed. Closing PR #5775 and removing active labels.