RFR: 7902698: Collision of zero timestamp as a special value with use in filesystems

[Liam Miller-Cushon]

On Thu, 20 Jan 2022 03:27:00 GMT, Liam Miller-Cushon <cushon at openjdk.org> wrote:

> This fixes a bug when the timestamp of a test file is set to zero, since jtharness currently uses zero as a special value. See discussion in [CODETOOLS-7902698](https://bugs.openjdk.java.net/browse/CODETOOLS-7902698).

Thanks for the review!

> It possibly would be more reliable and readable to switch types of these fields from 'long' to OptionalLong with OptionalLong.empty() as their default value.

Done

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PR: https://git.openjdk.java.net/jtharness/pull/22