anchor.diff:      return node;
     }
   }
  +class _ProjectDependencies {
  +  final Project project;
  +  final Set<Project> directDependencies;
   
  -class _DependencyNode {
  +  _ProjectDependencies(this.project, this.directDependencies);
  +}
  +
  +class _DependencyNode implements _ProjectDependencies {
     final Project project;
     final Set<_DependencyNode> _dependencies;
     Iterable<Project> get directDependencies =>
  
positive.code: 
    Map<Project, _DependencyNode> _nodeMap = {};
  
    DependencyGraph._(Set<_DependencyNode> dependencySet) {
      dependencySet.forEach((ds) => _add(ds.project, ds.directDependencies));
    }
  
  
negative.code:       .where((v) => v != null)
        .toSet();
  
    return new _ProjectDependencies(project, dependencies);
  }
  