docs: public boolean isPredicatesOptimizableForAggregate() {
          // for reverse scan, need to examine "added" predicates
          List<AbstractExpression> predicates = ExpressionUtil.uncombinePredicate(m_predicate);
          // if the size of predicates doesn't equal 1, can't be our added artifact predicates
          if (predicates.size() != 1) {
              return false;
          }
          // examin the possible "added" predicates: NOT NULL expr.
          AbstractExpression expr = predicates.get(0);
          if (expr.getExpressionType() != ExpressionType.OPERATOR_NOT) {
              return false;
          }
          if (expr.getLeft().getExpressionType() != ExpressionType.OPERATOR_IS_NULL) {
              return false;
          }
          // Not reverse scan.
          if (m_lookupType != IndexLookupType.LT && m_lookupType != IndexLookupType.LTE) {
              return false;
          }
  
          return true;
      }