@Override
        public Node objectNode(ObjectNode node) {
            Map<StringNode, Node> result = new LinkedHashMap<>(node.size());
            for (Map.Entry<StringNode, Node> entry : node.getMembers().entrySet()) {
                result.put(entry.getKey().accept(this).expectStringNode(), entry.getValue().accept(this));
            }
            return new ObjectNode(result, node.getSourceLocation());
        }
Expands ${NAME} values inside of strings to a {@code System} property
or an environment variable.
smithy-build/src/main/java/software/amazon/smithy/build/model/SmithyBuildUtils.java