RFR: 8274232: Cleanup unnecessary null comparison before instanceof check in jdk.jdi

[Andrey Turbanov]

On Thu, 23 Sep 2021 18:04:34 GMT, Andrey Turbanov <duke at openjdk.java.net> wrote:

> Update code checks both non-null and instance of a class in jdk.jdi module classes.
> The checks and explicit casts could also be replaced with pattern matching for the instanceof operator. 
> Similar cleanups
> 1. [JDK-8273484](https://bugs.openjdk.java.net/browse/JDK-8273484) java.naming
> 2. [JDK-8258422](https://bugs.openjdk.java.net/browse/JDK-8258422) java.base

Yep.

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PR: https://git.openjdk.java.net/jdk/pull/5659