anchor.diff:  /// class AutocompleteFormExample extends State<AutocompleteFormExamplePage> {
   ///   final _formKey = GlobalKey<FormState>();
   ///   final TextEditingController _textEditingController = TextEditingController();
  -///   String _dropdownValue;
  -///   String _autocompleteSelection;
  +///   String? _dropdownValue;
  +///   String? _autocompleteSelection;
   ///
   ///   final List<String> _options = <String>[
   ///     'aardvark',
  
positive.code: ///                     child: Text(value),
  ///                   );
  ///                 }).toList(),
  ///                 validator: (String value) {
  ///                   if (value == null) {
  ///                     return 'Must make a selection.';
  ///                   }
  
negative.code: /// // An example of a type that someone might want to autocomplete a list of.
  /// class User {
  ///   const User({
  ///     required this.email,
  ///     required this.name,
  ///   });
  ///
  ///   final String email;
  