/**
* @return
*/
private TreeExpansionBroadcaster getTreeExpansionBroadcaster() {
if (treeExpansionBroadcaster == null) {
treeExpansionBroadcaster = new TreeExpansionBroadcaster(this);
renderer.addTreeExpansionListener(treeExpansionBroadcaster);
}
return treeExpansionBroadcaster;
}