comparing nulls

I am comparing the values in two tables, like

select count(*) from t1, t2
where

t1.a1 = t2.a2
t1.b1 = t2.b2
t1.c1 = t2.c2;

and all is well until say t1.b1 and t2.b2 are both null. Then the equality is not true.

Can someone tell me the correct way to write this without having to do something special for the nullable columns??

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