strimzi: Fix crash when the Kafka cluster list is still loading

[cesaroangelo]

Problem

Opening the Kafka Topics or Kafka Users page throws
Cannot read properties of null (reading 'map') and blanks the page.
It is reliably reproducible on a cluster that has no topics or users (the
lists render before the Kafka cluster list has resolved).

KubeObject.useList().items is typed Array<T> | null and is null while
the query is loading, but both list components mapped over it directly to
build the create-dialog namespace/cluster dropdowns.

Fix

• Normalise the cluster list to an array at the useList call site.
• Extract the dropdown derivations into null-tolerant helpers
  (clusterNamespaces, clusterNamesInNamespace) with unit tests covering
  the null/loading case, so the crash cannot silently regress.
• De-duplicate the shared KafkaClusterRef type into utils.

It's a small, self-contained change, and the null handling is covered by
unit tests. tsc, eslint, prettier and the full test suite (71 tests)
pass.

Note

This is a focused, standalone fix for the crash only. #850 also touches this
null crash, but bundles it with a v1-resources rework that has since landed
on main separately, and appears stale.

[Copilot]

Pull request overview

Fixes a Strimzi plugin crash on the Kafka Topics and Kafka Users pages that occurred when the Kafka cluster list was still loading (useList().items === null) and the UI attempted to .map() over it.

Changes:

• Added null-tolerant helpers for deriving namespaces and cluster names from a possibly-null cluster list, with unit tests for the loading/null case.
• Updated Kafka Topic/User list components to normalize useList().items to an array and reuse the shared helpers.
• Centralized the shared KafkaClusterRef type into src/utils/clusters.ts and updated component type imports.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
strimzi/src/utils/clusters.ts	Adds null-safe cluster list derivation helpers and shared KafkaClusterRef type.
strimzi/src/utils/clusters.test.ts	Unit tests covering null/loading and sorting/uniqueness behavior.
strimzi/src/components/TopicFormModal.tsx	Replaces local KafkaClusterRef type with shared utils type import.
strimzi/src/components/KafkaUserList.tsx	Normalizes useList results, uses shared helpers to avoid null crash.
strimzi/src/components/KafkaUserCreateFormModal.tsx	Replaces local KafkaClusterRef type with shared utils type import.
strimzi/src/components/KafkaTopicList.tsx	Normalizes useList results, uses shared helpers to avoid null crash.
strimzi/CHANGELOG.md	Documents the crash fix under Unreleased.

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[illume]

🎉 thanks!