RFR: 8342860: Fix more NULL usage backsliding

[theoweidmannoracle]

- Changed several "NULL" in comments to "null"
- Changed several `NULL` in code to `nullptr`

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Commit messages:
 - Fix copyright year
 - 8342860: Fix more NULL usage backsliding

Changes: https://git.openjdk.org/jdk/pull/21826/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21826&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342860
  Stats: 22 lines in 11 files changed: 0 ins; 0 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/21826.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21826/head:pull/21826

PR: https://git.openjdk.org/jdk/pull/21826