如何在Flutter中去除多余的BottomAppBar？

Scaffold(
  appBar: AppBar(
    title: Text('My App'),
  ),
  bottomNavigationBar: BottomAppBar(
    child: Container(),
  ),
  floatingActionButton: FloatingActionButton(
    onPressed: () {},
    child: Icon(Icons.add),
  ),
  floatingActionButtonLocation: FloatingActionButtonLocation.none,
)

Scaffold(
  appBar: AppBar(
    title: Text('My App'),
  ),
  body: Stack(
    children: [
      Positioned.fill(
        child: Center(
          child: Text('Content'),
        ),
      ),
      Positioned(
        bottom: 0,
        left: 0,
        right: 0,
        child: Visibility(
          visible: false, // 设置为false隐藏浮动按钮
          child: BottomAppBar(
            child: Container(),
          ),
        ),
      ),
      Positioned(
        bottom: 16,
        right: 16,
        child: FloatingActionButton(
          onPressed: () {},
          child: Icon(Icons.add),
        ),
      ),
    ],
  ),
)