It was using nullptr to signal that it was empty.

Bug: v8:10155
Change-Id: I0844d6a2bfacb1fd35ba83c24307de86f77f4e40
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2056470Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66271}