Backport "Do not assume left is non-null if another branch is null in splitLast" to 3.8.0#24402

WojciechMazur merged 3 commits intorelease-3.8.0scala/scala3:release-3.8.0from

release-3.8.0_backport-24325scala/scala3:release-3.8.0_backport-24325Copy head branch name to clipboard