RFR: 8374149: [bworld] Define and use new null checking API

[Vicente Romero]

Definition and use of a new null checking API

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Commit messages:
 - minor changes
 - additional changes to Checks
 - Merge branch 'bworld' into JDK-8374149
 - additional changes
 - Merge branch 'bworld' into JDK-8374149
 - 8374149: [bworld] Define and use new null checking API

Changes: https://git.openjdk.org/valhalla/pull/1859/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1859&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374149
  Stats: 206 lines in 12 files changed: 196 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/valhalla/pull/1859.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1859/head:pull/1859

PR: https://git.openjdk.org/valhalla/pull/1859