public void undo(StudentModel model) {
System.out.println("Undoing add command.");
int index = model.findIndexByElement(node);
if (index >= 0) ModelUtils.removeElement(model.getElement(index), model, true);
}
public Add(Node node, StudentModel model) {
this.node = node;
if (!model.getHistory().isEmpty() && model.getHistory().peek() instanceof Drag)
model.removeActionFromHistory();
}