icon property
If this is null, then if error is false, then default value is
CommonAlertDialogThemeData.successfulIcon Data and Color,
if it is null the default value is Icons.check_circle_outline, with
color, Colors.lightGreen, while in case error is true, default value is
CommonAlertDialogThemeData.errorIcon Data and Color, if it is null
the default value is Icons.block with color, Colors.red.
Implementation
final Icon? icon;