private @NotNull List<FoldRegion> getWindowRegions(@NotNull List<? extends FoldRegion> hostRegions) {
    List<FoldRegion> result = new ArrayList<>();
    hostRegions.forEach(hr -> {
      FoldingRegionWindow wr = getWindowRegion(hr);
      if (wr != null) {
        result.add(wr);
      }
    });
    return result;
  }
private @NotNull List<FoldRegion> getWindowRegions(@NotNull List<? extends FoldRegion> hostRegions)