Fix nil pointer dereference in ValidateClusterUpdate when old cluster is nil

[Debasish-87]

Fix nil pointer dereference in ValidateClusterUpdate when old cluster is nil

ValidateClusterUpdate currently assumes that the old cluster is non-nil and
dereferences old.Spec.EtcdClusters without a guard, which can lead to a panic
when old is nil.

This scenario can occur during validation flows where an old cluster object
is not provided (e.g., certain initialization or fuzz testing paths).

This change adds a nil check for the old cluster and safely returns the
validation results for the new cluster when old is nil. This prevents the
panic while preserving existing validation behavior.

A unit test has been added to ensure that ValidateClusterUpdate handles a
nil old cluster without panicking.

Fixes #18097

/release-note
Fix a nil pointer dereference in ValidateClusterUpdate when old cluster is nil, preventing a potential panic during cluster validation.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign justinsb for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

Welcome @Debasish-87!

It looks like this is your first PR to kubernetes/kops 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes/kops has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[k8s-ci-robot]

Hi @Debasish-87. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-ci-robot]

@Debasish-87: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

Details

In response to this:

/ok-to-test

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[Debasish-87]

Hi @hakman @zetaab,

Gentle ping for review when you have time.

This PR adds a nil check in ValidateClusterUpdate to prevent a potential panic when the old cluster is nil, along with a unit test to cover the case.

Also, could someone take a look and mark /ok-to-test so CI can proceed?

Thanks.