if (!hashNodeMap1.keySet().equals(hashNodeMap2.keySet())) {
return null;
}
matchingGroups = new HashMap<Set<BNode>, Set<BNode>>();
IntIterator hashIter = hashNodeMap1.keySet().intIterator();
while (hashIter.hasNext()) {
int hash = hashIter.next();
Set<BNode> nodes1 = hashNodeMap1.get(hash);
Set<BNode> nodes2 = hashNodeMap2.get(hash);
if (nodes1.size() != nodes2.size()) {
return null;
}