Integrated: 8314913: [lw5] null restrictions can only be applied to value classes

[Vicente Romero]

according to last iteration of the spec null restrictions can only be applied to value classes that declares an implicit constructor

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Commit messages:
 - Update ValueObjectCompilationTests.java
 - 8314913: [lw5] null restrictions can only be applied to value classes

Changes: https://git.openjdk.org/valhalla/pull/916/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=916&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314913
  Stats: 214 lines in 14 files changed: 80 ins; 34 del; 100 mod
  Patch: https://git.openjdk.org/valhalla/pull/916.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/916/head:pull/916

PR: https://git.openjdk.org/valhalla/pull/916