code: func ValidateAPIServer(a *kubeadm.APIServer, fldPath *field.Path) field.ErrorList {
  	allErrs := field.ErrorList{}
  	allErrs = append(allErrs, ValidateCertSANs(a.CertSANs, fldPath.Child("certSANs"))...)
  	return allErrs
  }
docs: // ValidateAPIServer validates a APIServer object and collects all encountered errors