private static String nodeNames(final Set<TopologyDescription.Node> nodes) {
        final StringBuilder sb = new StringBuilder();
        if (!nodes.isEmpty()) {
            for (final TopologyDescription.Node n : nodes) {
                sb.append(n.name());
                sb.append(", ");
            }
            sb.deleteCharAt(sb.length() - 1);
            sb.deleteCharAt(sb.length() - 1);
        } else {
            return "none";
        }
        return sb.toString();
    }
Returns the topic names for any optimized source changelogs
streams/src/main/java/org/apache/kafka/streams/processor/internals/InternalTopologyBuilder.java