Querying Through NUll

hello ,

I have 2 tables that are linked and i am querying sencond table from 1st table here is how my query looks. It works fine when i enter the parameter value from 1st table , it gives me the assoaciated values in 2nd table, But i also want it to display without filtering the second table when the parameter value is NULL ie when there are no associated values in 1st table. I tried putting "IS NULL" but it doest work. Can any one please help me out with this



Thx

SELECT DISTINCT dbo.group_primary.site_group_primary
FROM dbo.group_primary INNER JOIN
dbo.group_conversion ON dbo.group_primary.id = dbo.group_conversion.primary_group_id INNER JOIN
dbo.group_secondary ON dbo.group_conversion.secondary_group_id = dbo.group_secondary.id
WHERE (dbo.group_secondary.site_group_secondary = @secondary) OR
(dbo.group_secondary.site_group_secondary IS NULL)