fix: NPE in handleRecentResourceUpdate for an unknown secondary resource

[csviri]

ExternalResourceCachingEventSource.handleRecentResourceUpdate checks
that the primary has an entry in the cache, but then dereferences the
per-secondary lookup without checking it:

R actualResource = actualValues.get(resourceId);
if (actualResource.equals(previousVersionOfResource)) {

actualValues.get(resourceId) returns null whenever the primary has a
cache entry but that particular secondary id is not in it, which throws a
NullPointerException. This is reachable from
AbstractEventSourceHolderDependentResource.onUpdated for any
RecentOperationCacheFiller event source, e.g. after an update whose
resource id is not the one currently cached for that primary.

Skips the cache update when the resource is not tracked, which matches
the intent of the surrounding "only overwrite if we still hold the
version the caller saw" check.

Adds a regression test that fails with NullPointerException without this
change.

Part of #3517

[Copilot]

Pull request overview

Fixes a NullPointerException in ExternalResourceCachingEventSource.handleRecentResourceUpdate when a primary is cached but the specific secondary resource ID is not tracked, aligning behavior with the intended “only overwrite if the cached value matches the caller’s previous version” semantics.

Changes:

• Guarded the equality check in handleRecentResourceUpdate to avoid dereferencing a missing cached secondary entry.
• Added a regression test ensuring updates for unknown secondary resources are ignored (and do not throw).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/ExternalResourceCachingEventSource.java	Adds a null check before comparing cached vs previous resource to prevent NPE and skip untracked secondary updates.
operator-framework-core/src/test/java/io/javaoperatorsdk/operator/processing/event/source/ExternalResourceCachingEventSourceTest.java	Adds a regression test covering the “unknown secondary ID” update scenario.