code: public static void addLayerToMap(@NonNull MapboxMap mapboxMap, @NonNull Layer layer,
                                     @Nullable String idBelowLayer) {
      if (layer != null && mapboxMap.getStyle().getLayer(layer.getId()) != null) {
        return;
      }
      if (idBelowLayer == null) {
        mapboxMap.getStyle().addLayer(layer);
      } else {
        mapboxMap.getStyle().addLayerBelow(layer, idBelowLayer);
      }
    }
docs: Generic method for adding layers to the map.
  
  @param mapboxMap    that the current mapView is using
  @param layer        a layer that will be added to the map
  @param idBelowLayer optionally providing the layer which the new layer should be placed below
  @since 0.8.0