code: protected Filter getTransactionFilter(Transaction tx, ScanType type, Filter filter) {
      return TransactionFilters.getVisibilityFilter(tx, ttlByFamily, allowEmptyValues, type, filter);
    }
docs: Derived classes can override this method to customize the filter used to return data visible for the current
  transaction.
  
  @param tx the current transaction to apply
  @param type the type of scan being performed