Credits Without Sort Codes By Primary Provider

We have discovered that some credit entries were entered without specifying a Sort Code, which we need for reporting purposes. I need a total amount of such credits, by provider.

SELECT
 r.provcode,
 r.provlname,
 SUM(amount) AS "TotalCredits"
FROM
 sos.journal j,
 sos.patients p,
 sos.providers r
WHERE
 j.ptnum=p.ptnum AND
 p.providernum=r.providernum AND
 j.trandate BETWEEN '2000-03-01' AND '2016-03-15' AND
 j.sortcode IS NULL
GROUP BY
 r.provcode, r.provlname