Fix NPE in ManagedInformerEventSource

[Donnerbart]

Fixes #3331

[Copilot]

Pull request overview

Fixes a null-handling gap in the informer-managed update path where Fabric8 edit() can return null (notably on HTTP 404), which previously could lead to an NPE when updating the temporary resource cache. This aligns behavior with the reported issue #3331 (“patch target already deleted”).

Changes:

• Add a null guard in ManagedInformerEventSource.eventFilteringUpdateAndCacheResource to skip cache update when the update operation returns null.
• Add regression tests covering null returns from the update method at both the informer event source layer and via ResourceOperations.removeFinalizer.
• Minor test refactors/formatting adjustments.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/informer/ManagedInformerEventSource.java	Adds null-guard around cache update after updateMethod.apply(...); also changes manager() visibility.
operator-framework-core/src/test/java/io/javaoperatorsdk/operator/processing/event/source/informer/InformerEventSourceTest.java	Adds regression test ensuring eventFilteringUpdateAndCacheResource cleanly propagates null.
operator-framework-core/src/test/java/io/javaoperatorsdk/operator/api/reconciler/ResourceOperationsTest.java	Adds integration-style regression test for removeFinalizer when underlying patch/edit returns null.