anchor.diff:        ..sourceFactory = sourceFactory;
   
       if (packageMeta.isSdk) {
  -      libraries.addAll(getSdkLibrariesToDocument(sdk, context));
  +      libraries
  +          .addAll(new Set()..addAll(getSdkLibrariesToDocument(sdk, context)));
       }
   
       List<Source> sources = [];
  
positive.code:   ];
  }
  
  /// Generates Dart documentation for all public Dart libraries in the given
  /// directory.
  class DartDoc {
  
negative.code: 
  final String defaultOutDir = p.join('doc', 'api');
  
  /// Initialize and setup the generators.
  Future<List<Generator>> initGenerators(String url, List<String> headerFilePaths,
      List<String> footerFilePaths, String relCanonicalPrefix,
  