anchor.diff:    ///
     /// When [build] is called, the type is built, stored into this field,
     /// and set for the [node].
  -  DartType? _type;
  +  FunctionType? _type;
   
     FunctionTypeBuilder(
       this.typeFormals,
  
positive.code: 
    @override
    DartType build() {
      if (_type != null) {
        return _type!;
      }
  
      for (var typeParameter in typeFormals) {
  
negative.code: import 'package:analyzer/src/dart/ast/extensions.dart';
  import 'package:analyzer/src/dart/element/element.dart';
  import 'package:analyzer/src/dart/element/type.dart';
  import 'package:analyzer/src/dart/element/type_algebra.dart';
  import 'package:analyzer/src/dart/element/type_visitor.dart';
  import 'package:analyzer/src/summary2/type_builder.dart';
  
  