NOT Null constraint on foreign table not working

create database foo;

\c foo

create table foo_test ( a int );

\c postgres

create extension if not exists postgres_fdw;

create server foo_server foreign data wrapper postgres_fdw options ( dbname  'foo' );

create user mapping for current_user server foo_server;

create foreign table foo_test ( a int not null) server foo_server;

-- insert should return error for because NOT NULL constraint on column a

postgres=# insert into foo_test values ( null );

INSERT 0 1

postgres=# select * from foo_test;

 a 

---

  

(1 row)

-- clean up

drop foreign table foo_test;

drop server foo_server cascade;

\c postgres

drop database foo;