RFR: 8280743: HSDB "Monitor Cache Dump" command might throw NPE [v2]

[Serguei Spitsyn]

On Mon, 21 Aug 2023 21:26:11 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> ObjectMonitor.object() can be null so we need to defend against it. This bug was discovered by code inspection while working on [JDK-8280555](https://bugs.openjdk.org/browse/JDK-8280555).  We have no test for this, and I'm not sure how to reproduce this with HSDB like the [JDK-8280555](https://bugs.openjdk.org/browse/JDK-8280555) test did.  I did at least verify that the HSDB "Monitor Cache Dump" feature still works after this fix, although none of the monitors had a null object.
>
> Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Move fetching the Oop to inside the else block.

Looks good and safe to fix. :)
Thanks,
Serguei

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Marked as reviewed by sspitsyn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15369#pullrequestreview-1590545348