anchor.diff:  
     Future execute(ProjectCommand command,
         {ProjectFilter filter: _noOpFilter}) async {
  +    final _filter = filter != null ? filter : _noOpFilter;
       return await _processDependenciesDepthFirst((Project project,
           Iterable<Project> dependencies) async {
  -      if (filter(project)) {
  +      if (_filter(project)) {
           return await command.process(project, dependencies: dependencies);
         }
       });
  
positive.code:   Future executeAll(CompositeProjectCommand composite,
        {CommandConcurrencyMode concurrencyMode: CommandConcurrencyMode.concurrentCommand,
        ProjectFilter filter: _noOpFilter}) async {
      if (concurrencyMode != CommandConcurrencyMode.serial &&
          composite.commands
              .every((c) => c.concurrencyMode != CommandConcurrencyMode.serial)) {
        return _executeAllOnConcurrentProjects(composite, filter);
      } else {
        return _executeSerially(composite, filter);
      }
  
      // TODO: add support for concurrentCommand
  
negative.code:   @override
    Future executeOnGraph(ProjectDependencyGraphCommand command,
        {ProjectFilter filter: _noOpFilter}) async {
      final _filter = filter != null ? filter : _noOpFilter;
      final DependencyGraph graph =
          await getDependencyGraph(await _projectGroup.allProjects);
      return await command.process(
          graph, _projectGroup.containerDirectory, _filter);
    }
  }
  
  