class AncestorChildExpansionIterator implements SortedKeyValueIterator<Key,Value> {

    @Override
    public Value getTopValue() {
        if (!seeked) {
            throw new IllegalStateException("cannot getTopKey(), iterator has not been seeked");
        }
        
        if (topValue == null) {
            throw new NoSuchElementException("top value does not exist");
        }
        
        return topValue;
    }

    public  AncestorChildExpansionIterator(SortedKeyValueIterator<Key,Value> iterator, List<String> children, Equality equality);

}