RFR: 8327171: Fix more NULL usage backsliding

[David Holmes]

On Sun, 3 Mar 2024 05:19:45 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

> Please review this trivial change that replaces some recently introduced uses
> of NULL with nullptr.
> 
> Testing: mach5 tier1

Good and trivial. Thanks for fixing.

Did we not establish if there was a way to poison NULL so this backsliding can't happen?

-------------

Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18096#pullrequestreview-1913142780