@Override
  public @Nullable Element getState() {
    if (myAssociations.isEmpty()) return null;
    
    Element element = new Element("state");
    for (VirtualFilePointer pointer : myAssociations.keySet()) {
      final Element e = new Element("file");
      e.setAttribute("url", pointer.getUrl());
      final VirtualFilePointerContainer container = myAssociations.get(pointer);
      container.writeExternal(e, "association", false);
      element.addContent(e);
    }
    return element;
  }
@Override
  public @Nullable Element getState()