RFR: 8338874: [lw5] add nullable types [v3]

[Vicente Romero]

> adding support for nullable types

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

  additional changes

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1219/files
  - new: https://git.openjdk.org/valhalla/pull/1219/files/de355909..eb0e2c00

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1219&range=02
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1219&range=01-02

  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/valhalla/pull/1219.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1219/head:pull/1219

PR: https://git.openjdk.org/valhalla/pull/1219