fix: handle nil values in field path and update tests

[TwoStone]

Summary

Fixes a nil pointer dereference panic that occurs when GetFrom attempts to access fields from embedded structs that are nil pointers. This adds defensive nil checking when traversing field paths to safely return zero values instead of panicking.

Problem

The FieldCacheEntry.GetFrom method in value/reflectcache.go traverses field paths using FieldByIndex without checking if intermediate struct values are nil. When dealing with embedded pointer structs (e.g., *testBasicStruct embedded with ,inline tag), if the pointer is nil, calling FieldByIndex causes a panic.

Example scenario:

type testEmbeddedStruct struct {
    *testBasicStruct `json:",inline"`
}

// When testBasicStruct is nil, accessing its fields would panic
val := testEmbeddedStruct{} // embedded pointer is nil

Impact

• No breaking changes: Existing behavior preserved for non-nil paths
• Bug fix: Prevents panic when accessing fields through nil embedded struct pointers
• Graceful degradation: Returns appropriate zero values instead of crashing

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[TwoStone]

Hi @liggitt and a happy new year - i hope you are the right to mention here - i just wanted to ask if you can give an estimation when the PR can get a first review.

[AndrewChubatiuk]

fixes kubernetes-sigs/controller-runtime#3418

[TwoStone]

Hello, is threre a chance to get a feedback to this PR? Thanks in advance
@jpbetz @liggitt @Jefftree @yliaog @cici37 @yongruilin

[jpbetz]

/approve
/lgtm

Thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jpbetz, TwoStone

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[alvaroaleman]

@jpbetz this fix is needed to make it possible to use the fakeclient in controller runtime with an api that embedds a struct pointer. Is there any chance this could be backported into k8s 1.35?

[liggitt]

Any project can require this version of this dependency without needing k8s to bump, right?

[alvaroaleman]

Any project can require this version of this dependency without needing k8s to bump, right?

Oh you are right. Controller-Runtime actually has a direct dependency on it nowadays so we can bump that and thus pass the bump on to downstream projects. Thanks for the suggestion!