NULL is ambiguous in the DESC Default column output

CREATE TABLE t (c1 VARCHAR(10) NOT NULL, c2 VARCHAR(10) DEFAULT NULL, c3 VARCHAR(10) NOT NULL DEFAULT 'NULL');

Query OK, 0 rows affected (0.06 sec)

mysql [localhost] {msandbox} (test) > DESC t;

+-------+-------------+------+-----+---------+-------+

| Field | Type        | Null | Key | Default | Extra |

+-------+-------------+------+-----+---------+-------+

| c1    | varchar(10) | NO   |     | NULL    |       |

| c2    | varchar(10) | YES  |     | NULL    |       |

| c3    | varchar(10) | NO   |     | NULL    |       |

+-------+-------------+------+-----+---------+-------+