[SQL-DS-CACHE-89][POAE7-1016] Fix agg result when column value could be null

[jikunshang]

What changes were proposed in this pull request?

Fix agg result when column value could be null, previous behavior will evaluate this null value.

How was this patch tested?

manual tests, for a column which data could be null, select count(*), count(column_name) from table result would be different.

[github-actions]

#89

[jikunshang]

@xieqi @winningsix @iyupeng Please take a review, thanks.

[iyupeng]

Sorry for the late review:

• nullVector is not set in sum, min, max, and count
• sum, min, max should take account that all input values may be null

[jikunshang]

Sorry for the late review:

• nullVector is not set in sum, min, max, and count
• sum, min, max should take account that all input values may be null

Thanks for your comments, will address these in another pr.