code: func ValidateServiceUpdate(service, oldService *api.Service) field.ErrorList {
  	allErrs := ValidateObjectMetaUpdate(&service.ObjectMeta, &oldService.ObjectMeta, field.NewPath("metadata"))
  
  	if api.IsServiceIPSet(oldService) {
  		allErrs = append(allErrs, ValidateImmutableField(service.Spec.ClusterIP, oldService.Spec.ClusterIP, field.NewPath("spec", "clusterIP"))...)
  	}
  
  	allErrs = append(allErrs, ValidateService(service)...)
  	return allErrs
  }
docs: // ValidateServiceUpdate tests if required fields in the service are set during an update