Running reflect.ValueOf(X) where X is a nil interface will return
a zero Value. We cannot get the type (because no concrete type is
known) and cannot check if the Value is nil later on due to the way
reflect.Value works. So we should handle this case by immediately
returning nil. We cannot type-assert a nil interface to another
interface type (as no concrete type is assigned), so we must add
another check to see if the returned interface is nil.
This commit wires together the graceful delete option for pods
on the Kubelet. When a pod is deleted on the API server, a
grace period is calculated that is based on the
Pod.Spec.TerminationGracePeriodInSeconds, the user's provided grace
period, or a default. The grace period can only shrink once set.
The value provided by the user (or the default) is set onto metadata
as DeletionGracePeriod.
When the Kubelet sees a pod with DeletionTimestamp set, it uses the
value of ObjectMeta.GracePeriodSeconds as the grace period
sent to Docker. When updating status, if the pod has DeletionTimestamp
set and all containers are terminated, the Kubelet will update the
status one last time and then invoke Delete(pod, grace: 0) to
clean up the pod immediately.