How to remove back button from show bottom sheet?

[Falak Sabbir]

I am using show bottom sheet. But when I open show bottom sheet, in appbar back button is always showing. Automatically a back button appears. How to remove this back button from appbar? I am using like this:

new RaisedButton(
  child: new Text(
      'Click',
  ),
  color: Color.fromRGBO(2,49,75,1.0),
  elevation: 0.0,
  onPressed: _showBottomSheet,
)

_showBottomSheet(){
setState(() {
  _showBottomSheetCallBack = null;
});
_scaffoldKey.currentState.showBottomSheet<Null>((BuildContext context) {
  return new Container(
      child: new Column(
    mainAxisSize: MainAxisSize.min,
    children: <Widget>[
      new Padding(
          padding: const EdgeInsets.all(16.0),
          child: new Text(
            'Persistent header for bottom bar!',
            textAlign: TextAlign.left,
          )),
    ],
  ));
}).closed.whenComplete((){
  if(mounted){
    setState(() {
      _showBottomSheetCallBack = _showBottomSheet;
    });
  }
});
}