@Override
	public void undo() {
		if (oldKey == null) {
			if (newKey == null) {
				// Do Nothing, since this should never happen.
			} else {
				tree.removeAttribute(newKey);
			}
		} else {
			if (newKey == null) {
				tree.setAttribute(oldKey, oldValue, oldReadOnly);
			} else {
				if (!oldKey.equals(newKey)) {
					tree.removeAttribute(newKey);
				}
				tree.setAttribute(oldKey, oldValue, oldReadOnly);
			}
		}
		
		Outliner.documentAttributes.configureAndShow(tree);
	}