How to add rounded corners to BottomAppBar with CircularNotchedRectangle in Flutter

I want to create BottomAppBar with rounded corners, circular notched rectangle and material shadow. The problem is that when I add rounded corners to BottomAppBar by wrapping it with ClipRRect widget I lose material shadow.

BottomAppBar without rounded corners, but with Material shadow. Please ignore wrong aligned notch.

BottomAppBar wrapped in ClipRRect widget, but without shadow. Again please ignore wrong aligned notch:

How to achieve rounded corners with notch and material shadow?

Full code:

import 'package:flutter/material.dart';

void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: Scaffold(
        extendBody: true,
        body: Container(
          color: Colors.amber,
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
        floatingActionButton: Transform.translate(
          offset: Offset(0, -10),
          child: FloatingActionButton(
            onPressed: () {},
            child: Icon(Icons.add),
            elevation: 2.0,
          ),
        ),
        bottomNavigationBar: BottomNavigationView(),
      ),
    );
  }
}

class BottomNavigationView extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Transform.translate(
      offset: Offset(0.0, -10),
      child: Container(
        margin: EdgeInsets.only(left: 20, right: 20),
        child: ClipRRect(
          borderRadius: BorderRadius.all(Radius.circular(30),
          ),
          child: BottomAppBar(
            shape: CircularNotchedRectangle(),
            child: Row(
              mainAxisSize: MainAxisSize.max,
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: <Widget>[
                Column(
                  mainAxisSize: MainAxisSize.min,
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Icon(Icons.accessibility_new),
                  ],
                ),
                _buildMiddleTabItem(),
                Column(
                  mainAxisSize: MainAxisSize.min,
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Icon(Icons.accessibility_new),
                  ],
                )
              ],
            ),
          ),
        ),
      ),
    );
  }

  Widget _buildMiddleTabItem() {
    return Expanded(
      child: SizedBox(
        height: 60,
        child: Column(
          mainAxisSize: MainAxisSize.min,
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            SizedBox(height: 24),
            Text(''),
          ],
        ),
      ),
    );
  }
}

You can create your own ShapeBorder.

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        extendBody: true,
        body: Container(
          color: Colors.amber,
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
        floatingActionButton: Transform.translate(
          offset: Offset(0, -10),
          child: FloatingActionButton(
            onPressed: () {},
            child: Icon(Icons.add),
            elevation: 2.0,
          ),
        ),
        bottomNavigationBar: BottomNavigationView(),
      ),
    );
  }
}

class BottomNavigationView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Transform.translate(
      offset: Offset(0.0, -10),
      child: Container(
        margin: EdgeInsets.symmetric(horizontal: 10),
        padding: EdgeInsets.symmetric(horizontal: 20),
        decoration: ShapeDecoration(
          color: Colors.white,
          shape: MyBorderShape(),
          shadows: [
            BoxShadow(
                color: Colors.black38, blurRadius: 8.0, offset: Offset(1, 1)),
          ],
        ),
        child: Row(
          mainAxisSize: MainAxisSize.max,
          mainAxisAlignment: MainAxisAlignment.spaceAround,
          children: <Widget>[
            Column(
              mainAxisSize: MainAxisSize.min,
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Icon(Icons.accessibility_new),
              ],
            ),
            _buildMiddleTabItem(),
            Column(
              mainAxisSize: MainAxisSize.min,
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Icon(Icons.accessibility_new),
              ],
            )
          ],
        ),
      ),
    );
  }

  Widget _buildMiddleTabItem() {
    return Expanded(
      child: SizedBox(
        height: 60,
        child: Column(
          mainAxisSize: MainAxisSize.min,
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            SizedBox(height: 24),
            Text(''),
          ],
        ),
      ),
    );
  }
}

class MyBorderShape extends ShapeBorder {
  MyBorderShape();

  @override
  EdgeInsetsGeometry get dimensions => EdgeInsets.zero;

  @override
  Path getInnerPath(Rect rect, {TextDirection textDirection}) => null;

  double holeSize = 70;

  @override
  Path getOuterPath(Rect rect, {TextDirection textDirection}) {
    print(rect.height);
    return Path.combine(
      PathOperation.difference,
      Path()
        ..addRRect(
            RRect.fromRectAndRadius(rect, Radius.circular(rect.height / 2)))
        ..close(),
      Path()
        ..addOval(Rect.fromCenter(
            center: rect.center.translate(0, -rect.height / 2),
            height: holeSize,
            width: holeSize))
        ..close(),
    );
  }

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection textDirection}) {}

  @override
  ShapeBorder scale(double t) => this;
}