anchor.diff:  
     /// Returns the [PackageView] instance for each package in [packages], using
     /// the latest stable version.
  +  ///
  +  /// If the package does not exist, it will return null in the given index.
     Future<List<PackageView>> getPackageViews(List<String> packages) async {
       // TODO: consider a cache-check first and batch-load the rest of the packages
       return await Future.wait(packages.map((p) => _getPackageView(p)));
  
positive.code:   Future close() async {}
  
    /// Returns the [PackageView] instance for [package] on its latest stable version.
    Future<PackageView> _getPackageView(String package) async {
      return await cache.packageView(package).get(() async {
        final p = await packageBackend.lookupPackage(package);
        if (p == null) return null;
  
        final version = p.latestVersion;
        final pvFuture = packageBackend.lookupPackageVersion(package, version);
  
negative.code:         .toList();
      final pubPackages = <String, PackageView>{};
      for (final view in await getPackageViews(packageNames)) {
        // The package may have been deleted, but the index still has it.
        if (view == null) continue;
        pubPackages[view.name] = view;
      }
  
  