如何在Flutter中丢弃FlatButton中的填充？

class CustomFlatButton extends FlatButton {
  const CustomFlatButton({
    Key key,
    @required VoidCallback onPressed,
    ButtonTextTheme textTheme = ButtonTextTheme.normal,
    Color textColor,
    Color disabledTextColor,
    Color color,
    Color disabledColor,
    Color focusColor,
    Color hoverColor,
    Color highlightColor,
    EdgeInsetsGeometry padding,
    ShapeBorder shape,
    Clip clipBehavior,
    MaterialTapTargetSize materialTapTargetSize,
    @required Widget child,
  }) : super(
          key: key,
          onPressed: onPressed,
          textTheme: textTheme,
          textColor: textColor,
          disabledTextColor: disabledTextColor,
          color: color,
          disabledColor: disabledColor,
          focusColor: focusColor,
          hoverColor: hoverColor,
          highlightColor: highlightColor,
          padding: padding,
          shape: shape,
          clipBehavior: clipBehavior,
          materialTapTargetSize: materialTapTargetSize,
          child: child,
        );

  @override
  Widget build(BuildContext context) {
    return super.build(context);
  }
}

@override
Widget build(BuildContext context) {
  final EdgeInsetsGeometry defaultPadding = ButtonTheme.of(context).padding;
  return ButtonTheme(
    padding: EdgeInsets.zero,
    minWidth: 0,
    child: FlatButton(
      onPressed: onPressed,
      textTheme: textTheme,
      textColor: textColor,
      disabledTextColor: disabledTextColor,
      color: color,
      disabledColor: disabledColor,
      focusColor: focusColor,
      hoverColor: hoverColor,
      highlightColor: highlightColor,
      padding: padding ?? defaultPadding,
      shape: shape,
      clipBehavior: clipBehavior,
      materialTapTargetSize: materialTapTargetSize,
      child: child,
    ),
  );
}

CustomFlatButton(
  onPressed: () {
    // 处理按钮点击事件
  },
  child: Text('按钮'),
),