allErrs := field.ErrorList{}
	count := int(0)
	if source.ConfigMap != nil {
		count++
		allErrs = append(allErrs, validateConfigMapNodeConfigSourceSpec(source.ConfigMap, fldPath.Child("configMap"))...)
	}
	// add more subfields here in the future as they are added to NodeConfigSource

	// exactly one reference subfield must be non-nil