code: func (l *kvLedger) NewHistoryQueryExecutor() (ledger.HistoryQueryExecutor, error) {
  	return l.historyDB.NewHistoryQueryExecutor(l.blockStore)
  }
docs: // NewHistoryQueryExecutor gives handle to a history query executor.
  // A client can obtain more than one 'HistoryQueryExecutor's for parallel execution.
  // Any synchronization should be performed at the implementation level if required
  // Pass the ledger blockstore so that historical values can be looked up from the chain