code: @Nullable
    public List<LineString> inner() {
      List<List<Point>> coordinates = coordinates();
      if (coordinates.size() <= 1) {
        return new ArrayList(0);
      }
      List<LineString> inner = new ArrayList<>(coordinates.size() - 1);
      for (List<Point> points : coordinates.subList(1, coordinates.size())) {
        inner.add(LineString.fromLngLats(points));
      }
      return inner;
    }
docs: Convenience method to get a list of inner {@link LineString}s defining holes inside the
  polygon. It is not guaranteed that this instance of Polygon contains holes and thus, might
  return a null or empty list.
  
  @return a List of {@link LineString}s defining holes inside the polygon
  @since 3.0.0