Need magical advice for counting NOTHING

Hi,
The source select counts log-events per user.
All is well when a user has at least one event per log_type in the log
within a given timespan.
If one log_type is missing COUNT() has nothing to count and there is
expectedly no result line that says 0.
BUT I need this 0-line because of a crosstab. :(
I need to know how to prevent in my crosstab categories on the right to
slip to the left, when the left category is emptyy.

Server 8.3.5

3 tables
log (log_id, log_type_fk, user_fk, ts timestamp, ...)
users (user_id, user_name, ...)
log_type (log_type_id, log_type)
There are 3 events as log_type.

I naively tried
SELECT user_name, log_type_fk, COUNT(log_type_fk)
FROM log
JOIN users ON (user_id = user_fk)
WHERE (ts IS BETWEEN sometime AND another)
GROUP BY user_name, log_type_fk
ORDER BY user_name, log_type_fk

This results e.g. to

user1, type1, 2
user1, type2, 3
user1, type3, 7
user2, type1, 11
user2, type3, 17

but I needed also
user2, type2, 0

How would I get there ?

Regards
Andreas