CONCAT doesn't work with NULL?

[Afan Pasalic]

hi,

I have query
SELECT CONCAT(r.first_name, ' ', r.last_name, '\n', r.organization, 
'\n', r.title, '\n', a.address1, '\n', a.city, ', ', a.state, ' ', 
a.zip, '\n', r.email)
FROM registrants r, addresses a
WHERE r.reg_id=121

if any of columns has value (e.g. title) NULL, I'll get as result 0 records.
If query doesn't have concat() - it works fine.

Why is that?

-afan