[4.15] volumesnapshot admission webhook doesn't reject invalid request

volumesnapshot admission webhook should block some invalid creatation like if volumeSnapshotClassName is ""
$ more storage/snapshot/invalid-volumesnapshot-snapshotclass-nil.yaml
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: mysnapshot
spec:
  volumeSnapshotClassName: ""
  source:
    persistentVolumeClaimName: mypvc-ori
    
In 4.16, it will be rejected as expected as below:
$ oc create -f storage/snapshot/invalid-volumesnapshot-snapshotclass-nil.yaml
Error from server: error when creating "storage/snapshot/invalid-volumesnapshot-snapshotclass-nil.yaml": admission webhook "volumesnapshotclasses.snapshot.storage.k8s.io" denied the request: Spec.VolumeSnapshotClassName must not be the empty string.


But in 4.15, it passed: 
$ oc create -f storage/snapshot/invalid-volumesnapshot-snapshotclass-nil.yaml 
volumesnapshot.snapshot.storage.k8s.io/mysnapshot created

And in the snapshot-webhook log, I did not see any log about mysnapshot:
$ oc -n openshift-cluster-storage-operator logs csi-snapshot-webhook-f996557d-c92rl | grep mysnapshot
$ oc -n openshift-cluster-storage-operator logs csi-snapshot-webhook-f996557d-nsnfg | grep mysnapshot    

4.15.0-0.nightly-2024-03-24-023440    

    always

See description     

    The invalid creation is not rejected in 4.15.

    The invalid creation should be rejected like in 4.16.