RFR: 8342860: Fix more NULL usage backsliding [v2]

[theoweidmannoracle]

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

theoweidmannoracle has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8342860
 - Fix copyright year
 - 8342860: Fix more NULL usage backsliding

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21826/files
  - new: https://git.openjdk.org/jdk/pull/21826/files/afb592f8..9754145b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21826&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21826&range=00-01

  Stats: 123205 lines in 577 files changed: 97665 ins; 8394 del; 17146 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