RFR: Generate missing null checks [v2]

[Vicente Romero]

> generate missing null checks like for method arguments, return arguments, etc

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

  record patterns

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1867/files
  - new: https://git.openjdk.org/valhalla/pull/1867/files/b676689c..c58a9cfd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1867&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1867&range=00-01

  Stats: 9 lines in 2 files changed: 5 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/valhalla/pull/1867.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1867/head:pull/1867

PR: https://git.openjdk.org/valhalla/pull/1867