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

[Andrey Turbanov]

On Sat, 5 Sep 2020 18:55:53 GMT, Andrey Turbanov <github.com+741251+turbanoff at openjdk.org> wrote:

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

I believe this changes is useful and still actual:
1. improve code to make it easier to read.
2. performance should be improved a bit too

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