Sequenced temporal min/max aggregation without group-by not SR

[lordpretzel]

The implementation is not returning NULL for empty snapshots:

SELECT * FROM (SEQUENCED TEMPORAL (SELECT max(salary) AS x FROM ttest WITH TIME (FROM_DATE, TO_DATE))) a ORDER BY T_B;

 X     | T_B        | T_E        |
----------------------------------
 41538 | 1988-09-05 | 1989-09-05 |
 45131 | 1989-09-05 | 1990-09-05 |
 45629 | 1990-09-05 | 1991-09-05 |
 48360 | 1991-09-05 | 1992-09-04 |
 50664 | 1992-09-04 | 1993-09-04 |
 53060 | 1993-09-04 | 1994-09-04 |
 56640 | 1994-09-04 | 1995-09-04 |
 53112 | 1998-04-11 | 1999-04-11 |
 53164 | 1999-04-11 | 1999-10-31 |