public Optional<String> apiVersion() {
        return Optional.ofNullable(this.apiVersion);
    }
@return APIVersion holds the API group and version of the referenced subject. Defaults to &#34;v1&#34; for ServiceAccount subjects. Defaults to &#34;rbac.authorization.k8s.io/v1alpha1&#34; for User and Group subjects.
sdk/java/src/main/java/com/pulumi/kubernetes/rbac/v1alpha1/outputs/Subject.java