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