RFR: Optional refactoring

[Aleksey Shipilev]

On Sun, 26 Mar 2023 08:38:53 GMT, Andrei Rybak <duke at openjdk.org> wrote:

> This is a follow-up to the email https://mail.openjdk.org/pipermail/jmh-dev/2023-January/003562.html
> 
> `java.util.Optional` isn't `Serializeable`. Because of that `org.openjdk.jmh.runner.options.TestOptions` fails with `java.io.NotSerializableException: java.util.Optional`, when  `org.openjdk.jmh.util.Optional` is completely replaced with `java.util.Optional`. See [test results on branch `java-util-optional`](https://github.com/rybak/jmh/actions/runs/4326921418), ([one commit](https://github.com/rybak/jmh/commit/25b9cb382be7285a51446976247d036ac855fc91) on top of initial state of this PR).
> 
> I didn't look further into possibility of removing `Optional`s as fields of class `CommandLineOptions`. I think that the refactoring up until the drop-in replacement to `java.util.Optional` might still be worth it, at least from the point of making it more approachable for people who are familiar with `java.util.Optional`.  So here are these changes for your consideration. Details are in the commit messages.

All right, then this would not work, unfortunately. Close this PR if you agree. We can always reopen it, if needed later.

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PR Comment: https://git.openjdk.org/jmh/pull/98#issuecomment-1486775921