RFR: 8297814: (fs) Re-visit Path.getExtension return value [v3]

[Brian Burkhalter]

On Fri, 20 Jan 2023 21:24:53 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Revise `java.nio.file.Path::getExtension` never to return `null` and to simplify implementing other path manipulations such as removing and replacing the file name extension.
>
> Brian Burkhalter has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:
> 
>  - Merge
>  - 8297814: Address reviewer comments
>  - 8297814: (fs) Re-visit Path.getExtension return value

This PR to be superseded by the work for https://bugs.openjdk.org/browse/JDK-8298318.

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PR: https://git.openjdk.org/jdk/pull/11545