[jdk21u-dev] RFR: 8340276: Test java/lang/management/ThreadMXBean/Locks.java failed with NullPointerException

[Bara' Hasheesh]

Backport JDK-8340276 for parity with oracle.

Clean backport, resolving a NPE problem in an existing test, tier1 & modified test pass after changes

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Commit messages:
 - Backport c58fbef05eace85a2e429da1ac8ff1ae09a0b736

Changes: https://git.openjdk.org/jdk21u-dev/pull/1918/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1918&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340276
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1918.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1918/head:pull/1918

PR: https://git.openjdk.org/jdk21u-dev/pull/1918