private void hide(Dockable dockable) {
		if (dockable == null) {
			throw new NullPointerException("dockable");
		}

		DockableContainer dockableContainer = DockingUtilities
				.findSingleDockableContainer(dockable);

		if (dockableContainer == null) {// ||
										// !dockingPanel.isAncestorOf((Component)
										// dockableContainer)){
			throw new IllegalArgumentException("not docked");
		}