public void ungroupCluster(Cluster cluster) {
   GraphModel gm = Lookup.getDefault().lookup(GraphController.class).getModel();
   if (gm != null) {
     HierarchicalGraph graph = gm.getHierarchicalGraphVisible();
     graph.ungroupNodes(cluster.getMetaNode());
     cluster.setMetaNode(null);
   }
 }
 public boolean canUngroup(Cluster cluster) {
   return cluster.getMetaNode() != null;
 }