anchor.diff:          }
         },
         onError: (e) {
  -        print(e);
           // Errors thrown by MongoDatabase are Map objects with fields err, code,
           // ...
           return _release_locks().then((_) {
  
positive.code:    */
    Future<Map> data() {
      Map selector = _selectorList.isEmpty ? {} : {AND: _selectorList};
      print(selector);
      return collection.find(selector).toList().then((data) {
        var version = data.length == 0 ? 0 :
          data.map((item) => item['__clean_version']).reduce(max);
  
negative.code:         }
        },
        onError: (e) {
          // Errors thrown by MongoDatabase are Map objects with fields err, code,
          // ...
          return _release_locks().then((_) {
  