RFR: 8374149: [bworld] Define and use new null checking API [v3]

[Vicente Romero]

> Definition and use of a new null checking API

Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:

  adding a flag

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1859/files
  - new: https://git.openjdk.org/valhalla/pull/1859/files/352e73a3..43b44fff

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1859&range=02
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1859&range=01-02

  Stats: 62 lines in 12 files changed: 53 ins; 0 del; 9 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