null value of type java.sql.Time

Occasionally I want to store a null value for my java.sql.Time--> Time
column in Postgresql.
update event set game_clock=null where event_id=1;

I can retreive the record with the null value (type Time) if I select
on the primary key,
select game_clock from event where event_id = 1;

but when I try to select on the null column value, I get zero records.
select * from event where game_clock=null;

How can I retreive records with null values for a column?
thanks,
Phil