anchor.diff:              isAsync: body.isAsynchronous, isStar: body.isGenerator));
     }
   
  +  ast.Expression buildOptionalTopLevelExpression(Expression node) {
  +    return node == null ? null : buildTopLevelExpression(node);
  +  }
  +
     ast.Expression buildTopLevelExpression(Expression node) {
       try {
         return _expressionBuilder.build(node);
  
positive.code:     for (var parameter in formals) {
        var declaration = makeVariableDeclaration(parameter.element,
            initializer: parameter is DefaultFormalParameter
                ? buildOptionalExpression(parameter.defaultValue)
                : null,
            type: buildType(parameter.element.type));
        switch (parameter.kind) {
  
negative.code:   }
  
    ast.Initializer buildInitializer(ConstructorInitializer node) {
      try {
        return new InitializerBuilder(this).build(node);
      } on _CompilationError catch (_) {
        return new ast.InvalidInitializer();
      }
    }
  
    bool isFinal(Element element) {
  