Query case sensitive in SQL database without setting database to case sensitive

Query case sensitive in SQL database without setting database to case
sensitive

I have a column IsSeeded with values 'N' and 'NULL' as one of the
possibilities I want to select all records that don't have a 'N' in their
field.
when I query
select * from database.file where IsSeeded !='N';
it also doesn't return the files with values 'NULL'. How can I allow
'NULL' values without having to change my databasepreferences to case
sensitive?
Thanks.
Vincent.