Can't add foreign key with empty referenced columns list

--source include/have_innodb.inc

CREATE TABLE t1(a INT PRIMARY KEY) ENGINE=InnoDB;

CREATE TABLE t2(a INT PRIMARY KEY) ENGINE=InnoDB;

ALTER TABLE t2 ADD FOREIGN KEY(a) REFERENCES t1;

DROP TABLE t2, t1;

mysqltest: At line 4: query 'ALTER TABLE t2 ADD FOREIGN KEY(a) REFERENCES t1' failed: 2013: Lost connection to MySQL server during query

...

mariadbd: /mariadb/10.5/storage/innobase/handler/ha_innodb.cc:12306: dberr_t create_table_info_t::create_foreign_keys(): Assertion `i == j' failed.