No warnings or errors after same sequential revoke

Hello!
Why we have no warnings or errors about that we have no such grant
after first revoke?
postgres=> grant select(i2) on table user1.t2 to user2;
GRANT
postgres=> revoke select(i2) on table user1.t2 from user2;
REVOKE
postgres=> revoke select(i2) on table user1.t2 from user2;
REVOKE
postgres=> revoke select(i2) on table user1.t2 from user2;
REVOKE
postgres=> revoke select(i2) on table user1.t2 from user2;
REVOKE

No warnings about that this grant is not available.
It looks like revoking nonexisting grants is allowed???

--
Alex Ignatov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company