It's a change in VFP9 which makes result of the query with SUM() ANSI Standard compliant. You can easily get what you want

SELECT CAST(NVL(SUM(T1),0) AS int) AS t1 FROM T1

>CREATE CURSOR T1(t1 I NOT NULL)
>SELECT SUM(T1) AS t1 FROM T1
>
>This returns a cursor with a single NULL value.
>
>Wouldn't it be better to return a 0? And by better I am thinking less likely to break my existing code.