null in constraints

Hello Hackers,

with V7.02, it seems when a constraint evalutes to 'null', it behaves
like 'true'. I'm rather sure this behaviour changed from V6.x, though I 
can't check it.

example:
 create table test (a int4 check (a > 0));

allows a to be null. But
 select * from test where a > 0;

doesn't return any null values.

Is this the intended behaviour?

cheers
Andreas