private static @NotNull FoldRegionImpl getRegion(@NotNull IntervalNode<FoldRegionImpl> node) {
      assert node.intervals.size() == 1;
      FoldRegionImpl region = node.intervals.get(0).get();
      assert region != null;
      return region;
    }
private static @NotNull FoldRegionImpl getRegion(@NotNull IntervalNode<FoldRegionImpl> node)