JSON_LENGTH returns incorrect length

MariaDB [test]> select json_length('{}');

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

| json_length('{}') |

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

|                 1 |

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

1 row in set (0.01 sec)

MariaDB [test]> SELECT JSON_LENGTH('[1, 2, {"a": 3}]');

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

| JSON_LENGTH('[1, 2, {"a": 3}]') |

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

|                               4 |

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

1 row in set (0.00 sec)

MySQL [test]> select json_length('{}');

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

| json_length('{}') |

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

|                 0 |

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

1 row in set (0.00 sec)

MySQL [test]> SELECT JSON_LENGTH('[1, 2, {"a": 3}]');

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

| JSON_LENGTH('[1, 2, {"a": 3}]') |

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

|                               3 |

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

1 row in set (0.01 sec)