Wrong result from ref_or_null access when two key parts have IS NULL alternatives

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

  INSERT INTO t1 VALUES (NULL,2);

  CREATE TABLE t2 (x INT) ENGINE=InnoDB;

  INSERT INTO t2 VALUES (2);

  SELECT (SELECT COUNT(*) FROM t2 AS i, t1

          WHERE (t1.a = 1 OR t1.a IS NULL) AND

                (t1.b = o.x OR t1.b IS NULL) AND

                t1.b = i.x) AS c

  FROM t2 AS o;

  SELECT (SELECT COUNT(*) FROM t2 AS i, t1 IGNORE INDEX(a)

          WHERE (t1.a = 1 OR t1.a IS NULL) AND

                (t1.b = o.x OR t1.b IS NULL) AND

                t1.b = i.x) AS c

  FROM t2 AS o;

  DROP TABLE t1, t2;