feat: allow to use null from clients side with primitives

[denis-anisimov]

fixes #4062

Description

Please list all relevant dependencies in this section and provide summary of the change, motivation and context.

Fixes # (issue)

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[vaadin-bot]

SonarQube analysis reported 8 issues

1. PublishedServerEventHandlerRpcHandler.java#L188: A "NullPointerException" could be thrown; "instance" is nullable here.
2. PublishedServerEventHandlerRpcHandler.java#L194: A "NullPointerException" could be thrown; "instance" is nullable here.
3. PublishedServerEventHandlerRpcHandler.java#L284: Refactor this method to reduce its Cognitive Complexity from 18 to the 15 allowed.
4. PublishedServerEventHandlerRpcHandler.java#L113: Remove this use of "PolymerServerEventHandlers"; it is deprecated.
5. PublishedServerEventHandlerRpcHandler.java#L114: Remove this use of "PolymerServerEventHandlers"; it is deprecated.
6. PublishedServerEventHandlerRpcHandler.java#L155: Replace this lambda with a method reference.
7. PublishedServerEventHandlerRpcHandler.java#L305: Remove this use of "DeprecatedPolymerPublishedEventHandler"; it is deprecated.
8. PublishedServerEventHandlerRpcHandler.java#L307: Remove this use of "DeprecatedPolymerPublishedEventHandler"; it is deprecated.

[vaadin-bot]

This ticket/PR has been released with platform 22.0.0.alpha6 and is also targeting the upcoming stable 22.0.0 version.