public Optional<String> namespace() {
        return Optional.ofNullable(this.namespace);
    }
@return Namespace of the referenced object.  If the object kind is non-namespace, such as &#34;User&#34; or &#34;Group&#34;, and this value is not empty the Authorizer should report an error.
sdk/java/src/main/java/com/pulumi/kubernetes/rbac/v1/outputs/Subject.java