RFR: 8258422: Cleanup unnecessary null comparison before instanceof check in java.base

[Andrey Turbanov]

On Mon, 11 Jan 2021 16:57:00 GMT, Aleksei Efimov <aefimov at openjdk.org> wrote:

>> 8258422: Cleanup unnecessary null comparison before instanceof check in java.base
>
> Hi @turbanoff,
> This PR is ready for integration - `JDK-8258657` has been resolved.
> You can proceed with issuing `integrate` bot command. Then I will `sponsor` it.
> But before that, I would like to ask if you would like to take on board the changes to `HttpClientImpl`? Alternatively, I can follow it up separately and reapply the backed-out change under different bugID.

@AlekseiEfimov `HttpClientImpl` is not in `java.base` module. So I think it's better to not touch it under this PR.

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PR: https://git.openjdk.java.net/jdk/pull/20