anchor.diff:    // variable.
     bool forLazyInitializer = false;
   
  -  js.Expression _value;
  -
  -  @override
  -  final js.JavaScriptNodeSourceInformation sourceInformation;
  +  js.Expression? _value;
  +
  +  @override
  +  final js.JavaScriptNodeSourceInformation? sourceInformation;
   
     TypeReference(this.typeRecipe) : sourceInformation = null;
     TypeReference._(this.typeRecipe, this._value, this.sourceInformation);
  
positive.code:   final RecipeEncoder _recipeEncoder;
    final bool _minify;
  
    /*late final*/ _TypeReferenceCollectorVisitor _visitor;
    TypeReferenceResource _resource;
  
    /// Maps the recipe (type expression) to the references with the same recipe.
    /// Much of the algorithm's state is stored in the _ReferenceSet objects.
  
negative.code:   }
  
    bool _dagCheck(DartType type) {
      int? ref = _backrefs[type];
      if (ref != null) {
        _add('\$$ref');
        return true;
  