static ZoomFunction<GeometryPipeline> compose(ZoomFunction<GeometryPipeline> a, GeometryPipeline b) {
    return zoom -> ZoomFunction.applyOrElse(a, zoom, NOOP).andThen(b);
  }
Returns a function equivalent to {@code b(a(geom))} at each zoom.
planetiler-core/src/main/java/com/onthegomap/planetiler/geo/GeometryPipeline.java