RFR: 8344917: Fix recent NULL usage backsliding

[Kim Barrett]

Please review this trivial fix of some recently introduced uses of NULL in HotSpot.

Testing:
mach5 tier1
GHA sanity tests

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Commit messages:
 - fix NULL backsliding

Changes: https://git.openjdk.org/jdk/pull/22348/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22348&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344917
  Stats: 9 lines in 7 files changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/22348.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22348/head:pull/22348

PR: https://git.openjdk.org/jdk/pull/22348