Composite Unique Key - Doubt

Team,

Am using Postgres 9.2

I am having a table

technologies
(
technologyid bigint,
status character(1),
implementeddate date
CONSTRAINT technologies_uq UNIQUE (technologyid, status, implementeddate)
)

entering data as

insert into technologies (technologyid,status,implementeddate)
values
(123,'P',null),
(123,'P',null);

2 rows affected.

table accepting duplicate values in spite of composite unique constraint..
where I am doing wrong?