Join condition in Oracle query - oracle

Question

I have following query which update the coulmn "tmp_activation_date" of rec_tmprecord table with max of actdate according to the conditions mentioned in query.
MERGE INTO rec_tmprecord
USING (SELECT rec.ID, MAX (act.actdate) AS tmpactivation_date
FROM rec_tmprecord rec INNER JOIN tmp_asset asset
ON asset.serial = rec.serialtemp
and upper (replace (asset.prodname, 'Ajink ')) = upper (replace (rec.prodnametemp, 'Ajink '))
and NVL(asset.release,'NF') = NVL(rec.tmprelease ,'NF')
and rec.serialtemp != 'aaa-aaaaaaaa'
LEFT JOIN tmp_acti_hist act
ON asset.tmp_id = act.tmp_row_id
WHERE rec.cust_id = 234567
GROUP BY rec.cust_id,asset.serial,rec.ID) new_values
ON (rec_tmprecord.ID = new_values.ID)
WHEN MATCHED THEN
UPDATE
SET tmp_activation_date = new_values.tmpactivation_date
;
But,When i analyzed the data of table "rec_tmprecord",i found that there are some null or blank values present in the "prodnametemp" column of "rec_tmprecord" table.But,column "prodname" of the table "tmp_asset" does not contain any null or blank values.
So,my join condition will fail at "upper (replace (asset.prodname, 'Ajink ')) = upper (replace (rec.prodnametemp, 'Ajink '))" condition and as a result "tmp_activation_date" of rec_tmprecord table will be updated with null value or blank value.
what my requirement is if "prodnametemp" is having null value and "prodname" contains some value then also "tmpactivation_date" will get calculated on the basis of other conditions mentioned in the query.
Anyhelp on this would be greatly appreciated.

Answer 1

Here is a modified version. I modified the join as follows:
upper (replace (asset.prodname, 'Ajink ')) = NVL(upper (replace (rec.prodnametemp, 'Ajink ')), upper (replace (asset.prodname, 'Ajink ')))
EDIT:
The join condition has been compressed, thanks to Alex Poole's suggestion.
Basically, if is NULL, then that condition would return TRUE, because then asset.prodname = asset.prodname.
MERGE INTO rec_tmprecord
USING (SELECT rec.ID, MAX (act.actdate) AS tmpactivation_date
FROM rec_tmprecord rec INNER JOIN tmp_asset asset
ON asset.serial = rec.serialtemp
and upper (replace (asset.prodname, 'Ajink ')) = upper (replace (NVL (rec.prodnametemp, asset.prodname), 'Ajink '))
and NVL(asset.release,'NF') = NVL(rec.tmprelease ,'NF')
and rec.serialtemp != 'aaa-aaaaaaaa'
LEFT JOIN tmp_acti_hist act
ON asset.tmp_id = act.tmp_row_id
WHERE rec.cust_id = 234567
GROUP BY rec.cust_id,asset.serial,rec.ID) new_values
ON (rec_tmprecord.ID = new_values.ID)
WHEN MATCHED THEN
UPDATE
SET tmp_activation_date = new_values.tmpactivation_date
;