RFR: 8310905: [lw5] addressing review comments on null restricted types [v6]

[Vicente Romero]

> addressing some review comments related to PR [1]
> 
> [1] https://github.com/openjdk/valhalla/pull/872

Vicente Romero has updated the pull request incrementally with two additional commits since the last revision:

 - addressing additional review comments
 - dont generate warnings for literals or constructor invocations

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/880/files
  - new: https://git.openjdk.org/valhalla/pull/880/files/054b5483..0c168ed2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=880&range=05
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=880&range=04-05

  Stats: 84 lines in 7 files changed: 58 ins; 15 del; 11 mod
  Patch: https://git.openjdk.org/valhalla/pull/880.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/880/head:pull/880

PR: https://git.openjdk.org/valhalla/pull/880