KObj should be able to handle nil objects

[ehashman]

What this PR does / why we need it:

Prevents klog.KObj from panicking when passed nil.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

See kubernetes/kubernetes#100109

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Release note:

KObj now supports nil objects

[logicalhan]

/lgtm
/approve

[DirectXMan12]

maybe as a follow-up we should consider either:

a) having object-ref's log representation explicitly report when it's completely empty to make this obvious
b) having KObj return a pointer such that a nil object becomes a nil object (I think this has perf implications though, so probably not)

"b" probably has allocation-related perf implications, so probably should do "a"

In the mean time, I think this is fine though -- prob better not to panic when a nil object is passed to a log line 😅

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: DirectXMan12, ehashman, logicalhan

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[serathius]

Because of differences between interface with nil value and just nil, I don't think this PR fixes the underlying issue. Full explanation kubernetes/kubernetes#100155