anchor.diff:    Db _db;
     LockRequestor _lockRequestor;
     Cache cache;
  +  bool _initialized = false;
   
     static const _dbLock = "dblock";
   
  
positive.code:         });
    }
  
    Future init() => _db.open();
  
    Future transact(callback(MongoDatabase _)) {
      Map meta = _lockRequestor.getZoneMetaData();
  
negative.code:    final StackTrace stackTrace;
     const MongoException(this.mongoError, this.stackTrace, [this.msg]);
     String toString() =>
         msg == null ?
             'MongoError: $mongoError \n Stack trace: $stackTrace' :
             '$msg MongoError: $mongoError \n Stack trace: $stackTrace';
  }
  
  class BreakException {
  