code: func GetPersistentVolumeClaimClass(claim *core.PersistentVolumeClaim) string {
  	// Use beta annotation first
  	if class, found := claim.Annotations[core.BetaStorageClassAnnotation]; found {
  		return class
  	}
  
  	if claim.Spec.StorageClassName != nil {
  		return *claim.Spec.StorageClassName
  	}
  
  	return ""
  }
docs: // GetPersistentVolumeClaimClass returns StorageClassName. If no storage class was
  // requested, it returns "".