RFR: 8324678: Replace NULL with nullptr in HotSpot gtests [v2]

[Coleen Phillimore]

> If this is sufficient, here's the change for NULL to nullptr, adjusting some obvious strings that had NULL in them maybe not all.
> Tested with gtest,

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Fix nullptr in comments and strings to null.  @kimbarrett changes.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/17577/files
  - new: https://git.openjdk.org/jdk/pull/17577/files/fefbd3d7..d8e3d92d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17577&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17577&range=00-01

  Stats: 15 lines in 8 files changed: 0 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/17577.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17577/head:pull/17577

PR: https://git.openjdk.org/jdk/pull/17577