anchor.diff:    final String name;
   
     ReadPropExpr(this.receiver, this.name, {OutputType outputType})
  -      : super(outputType);
  +      : super(outputType) {
  +    assert(name != null, 'Expecting name in ReadPropExpr');
  +  }
   
     @override
     dynamic visitExpression(ExpressionVisitor visitor, dynamic context) {
  
positive.code:       this.receiver, dynamic /* String | BuiltinMethod */ method, this.args,
        {OutputType outputType, this.checked})
        : super(outputType) {
      if (method is String) {
        this.name = method;
        this.builtin = null;
  
negative.code:   final List<OutputType> types;
  
    InstantiateExpr(this.classExpr, this.args, [OutputType type, this.types])
        : super(type) {
      assert(() {
        for (int len = args.length, i = 0; i < len; i++) {
          if (args[i] == null) {
            throw new ArgumentError('Expecting non-null arguments');
          }
        }
        return true;
      });
    }
  
    @override
    dynamic visitExpression(ExpressionVisitor visitor, dynamic context) {
  