Null and Not Null validation in Tmap

I am sending a main file into tmap. Then I have a lookup table from db to validate the brand_code from file. The column in the file can be null or not null. If not null then it has to be validated. If null then too it must be treated as valid value. So the output can have nulls.
I am using inner join in tmap. So that I can validate when there is a value in brand_code column. But if the column value is null then too its validating and rejecting that record.
Can anyone suggest a solution for the above issue.
Seven Stars

Re: Null and Not Null validation in Tmap

Change the tMap to left join and use an output expression filter like:
filerow.brand_code==null || lookuprow.brand_code!=null