code: private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
  		in.defaultReadObject();
  		final N me = toN();
  		if (this.nNorthEast != null) {
  			this.nNorthEast.setParentNodeReference(me, false);
  		}
  		if (this.nNorthWest != null) {
  			this.nNorthWest.setParentNodeReference(me, false);
  		}
  		if (this.nSouthEast != null) {
  			this.nSouthEast.setParentNodeReference(me, false);
  		}
  		if (this.nSouthWest != null) {
  			this.nSouthWest.setParentNodeReference(me, false);
  		}
  	}
docs: Invoked when this object must be deserialized.
  
  @param in is the input stream.
  @throws IOException in case of input stream access error.
  @throws ClassNotFoundException if some class was not found.