@Override
        public Node toNode() {
            return Node.objectNodeBuilder()
                    .withMember("resource", Node.from(resource.toString()))
                    .withOptionalMember("ids",
                            ids.isEmpty()
                                    ? Optional.empty()
                                    : Optional.of(ObjectNode.fromStringMap(getIds())))
                    .withOptionalMember("service", getService().map(ShapeId::toString).map(Node::from))
                    .withOptionalMember("rel", getRel().map(Node::from))
                    .build();
        }
@return Gets the optional rel property.
smithy-model/src/main/java/software/amazon/smithy/model/traits/ReferencesTrait.java