anchor.diff:      if (pv == null) return false;
   
       // Does package have any analysis?
  -    final List<PackageAnalysis> list =
  -        await db.lookup([db.emptyKey.append(PackageAnalysis, id: packageName)]);
  -    final PackageAnalysis packageAnalysis = list.first;
  +    final Key packageKey = db.emptyKey.append(PackageAnalysis, id: packageName);
  +    final PackageAnalysis packageAnalysis =
  +        (await db.lookup([packageKey])).single;
       if (packageAnalysis == null) return true;
   
       // Does package have newer version than latest analyzed version?
  
positive.code: 
      // Is latest analysis older than 4 hours?
      final DateTime now = new DateTime.now().toUtc();
      if (now.difference(versionAnalysis.analysisTimestamp).inHours < 4) {
        return false;
      }
  
  
negative.code: 
    Future deleteObsoleteAnalysisEntries() async {
      final DateTime threshold =
          new DateTime.now().toUtc().subtract(obsoleteThreshold);
      final Query query = db.query(Analysis)
        ..order('timestamp')
        ..filter('timestamp <', threshold);
  