@Override
    public String toString(final String indent) {
        final StringBuilder sb = new StringBuilder(super.toString(indent));
        sb.append(indent).append("\ttopic:\t\t");
        sb.append(topicExtractor);
        sb.append("\n");
        return sb.toString();
    }
@return a string representation of this node starting with the given indent, useful for debugging.
streams/src/main/java/org/apache/kafka/streams/processor/internals/SinkNode.java