private void unitePair(final T id1, final T id2) {
        final T root1 = root(id1);
        final T root2 = root(id2);

        if (!root1.equals(root2)) {
            ids.put(root1, root2);
        }
    }
@throws NoSuchElementException if the parent of this node is null
streams/src/main/java/org/apache/kafka/streams/processor/internals/QuickUnion.java