Concatenating NULL

CREATE TABLE myTable (
 id INT,
 string varchar(100) DEFAULT NULL
);
INSERT INTO myTable (id, string) VALUES (1, "First"), (2, NULL);
UPDATE myTable SET string = CONCAT(id, " has the value ", string);
SELECT * FROM myTable;

What is the output?

+------+-----------------------+
| id   | string                |
+------+-----------------------+
|    1 | 1 has the value First |
|    2 | NULL                  |
+------+-----------------------+