docs: @NonNull
    public static LineString lineSlice(@NonNull Point startPt, @NonNull Point stopPt,
                                       @NonNull Feature line) {
      if (line.geometry() == null) {
        throw new NullPointerException("Feature.geometry() == null");
      }
      if (!line.geometry().type().equals("LineString")) {
        throw new TurfException("input must be a LineString Feature or Geometry");
      }
      return lineSlice(startPt, stopPt, (LineString) line.geometry());
    }