whenOrNull<TResult extends Object?>  method 
    Null safety
- TResult? $default( )?,
- {TResult? byIndex( )?}
@optionalTypeArgs, inherited
    Implementation
@optionalTypeArgs
TResult? whenOrNull<TResult extends Object?>(
  TResult? Function(
          Key? key,
          bool selected,
          Callback? onSelect,
          Callback? onDeselect,
          Callback? onLongPress,
          MaterialStateProperty? color,
          List<DataCell> cells)?
      $default, {
  TResult? Function(
          int? index,
          bool selected,
          Callback? onSelect,
          Callback? onDeselect,
          Callback? onLongPress,
          MaterialStateProperty? color,
          List<DataCell> cells)?
      byIndex,
}) =>
    throw _privateConstructorUsedError;