Bottomexpandableappbar Fluttter how to make it work

Question

Guys good night, I’m having problem that I can not solve, I’m trying to add an expansive menu bar at the bottom of the screen and is not appearing when I run the code

 import 'dart:async';
 import 'package:expandable_bottom_bar/expandable_bottom_bar.dart';
 import 'package:flutter/material.dart';
 import 'package:google_maps_flutter/google_maps_flutter.dart';




  class Mapateste  extends StatefulWidget {
 @override
  State<Mapateste> createState() => MapatesteState();
 }

 class MapatesteState extends State<Mapateste> with 
 SingleTickerProviderStateMixin{
   BottomBarController controller;
   Completer<GoogleMapController> _controller = Completer();

  static final CameraPosition myhome = CameraPosition(
  target: LatLng(-23.195874, -45.883488),
  zoom: 14.4746,


);


 @override
  void initState() {
  super.initState();
  controller = BottomBarController(vsync: this, dragLength: 550, snap: 
  true);
}


@override
Widget build(BuildContext context) {
  return new Scaffold(   



  body: Stack( 

    children:<Widget>[


      GoogleMap(

        onMapCreated: (GoogleMapController controller){
          _controller.complete(controller);
        },
        mapType: MapType.normal,
        myLocationEnabled: true,
        initialCameraPosition: myhome,
        ),



      BottomExpandableAppBar(
        controller: controller, 
        expandedHeight: controller.dragLength,
        horizontalMargin: 16,
        expandedBackColor: Color.fromRGBO(16, 6, 144, 1),
      ),

    ],


   );

  }

 }