private void undo(Polygon polygon) {
LinearRing ring = null;
if (index.isExteriorRing()) {
ring = polygon.getExteriorRing();
LineString lineString = undo(ring);
setExteriorRing(polygon, (LinearRing) lineString);
} else if (index.getInteriorRingIndex() >= 0) {
ring = polygon.getInteriorRingN(index.getInteriorRingIndex());
LineString lineString = undo(ring);
setInteriorRingN(polygon, (LinearRing) lineString, index.getInteriorRingIndex());
}
}