build method Null safety

Implementation

@override
Widget build(BuildContext context) {
  if (mapElement.pointers.isEmpty || mapElement.pointers.first.geo == null) {
    return EMPTY_WIDGET;
  }
  // TODO(monsieurtanuki): Zoom the map to show all [mapElement.pointers]
  // TODO(monsieurtanuki): Add a OSM copyright.
  return Padding(
    padding: const EdgeInsets.only(bottom: MEDIUM_SPACE),
    child: SizedBox(
      height: 200,
      child: FlutterMap(
        options: MapOptions(
          // The first pointer is used as the center of the map.
          center: LatLng(
            mapElement.pointers.first.geo!.lat,
            mapElement.pointers.first.geo!.lng,
          ),
          zoom: 6.0,
        ),
        layers: <LayerOptions>[
          TileLayerOptions(
            urlTemplate: 'https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png',
            subdomains: <String>['a', 'b', 'c'],
          ),
          MarkerLayerOptions(
            markers: getMarkers(mapElement.pointers),
          ),
        ],
      ),
    ),
  );
}