code: @Override
    public N getNode(int nodeID) {
      N nID = supernodes.get(Long.valueOf(nodeID));
      if(nID != null) {
        return nID;
      }
      N n = super.getNode(nodeID);
      assert !n.isSuperNode(); // we should have them ALL in #supernodes
      return n;
    }
docs: Returns the node with the specified id. Note that supernodes are kept in
  main memory (in {@link #supernodes}, thus, their listing has to be tested
  first.
  
  @param nodeID the page id of the node to be returned
  @return the node with the specified id