RFR: 8340670: Policy.UNSUPPORTED_EMPTY_COLLECTION.isReadOnly does not return true

[Artur Barashev]

https://bugs.openjdk.org/browse/JDK-8340670

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Commit messages:
 - 8340670: Policy.UNSUPPORTED_EMPTY_COLLECTION.isReadOnly does not return true

Changes: https://git.openjdk.org/jdk/pull/21165/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21165&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340670
  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21165.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21165/head:pull/21165

PR: https://git.openjdk.org/jdk/pull/21165