Compound FK allows nulls - is that normal behaviour?

Database
Enthusiast

Compound FK allows nulls - is that normal behaviour?

Hello TeraData experts,

I've been surprised with the following behaviour of TD. Please see this example. Here are my tables:

create table mnagat.A (
a1 INTEGER,
a2 INTEGER)
UNIQUE PRIMARY INDEX ( a1, a2 )

create table mnagat.B (
b1 INTEGER,
b2 INTEGER,
FOREIGN KEY ( b1, b2 ) REFERENCES A ( a1 , a2 )
)

Statements like
insert into mnagat.B values (1, 1)
are rejected as expected when there's no such record in A.

But TD allows all these inserts, even when there's not any row on the A table:
insert into mnagat.B values (null, null)
insert into mnagat.B values (null, 1)
insert into mnagat.B values (1, null)

Shouldn't they be rejected by FK constraint (code 2700)?
Thanks.