first call of a stored procedure that uses session user variable always return NULL

[jennifersp]

Dolt server:

mysql>  CREATE PROCEDURE p1(x VARCHAR(20)) BEGIN SET @randomvar = (SELECT LENGTH(x)); SELECT @randomvar; END;#
mysql> delimiter ;
mysql> call p1('hi');
+------------+
| @randomvar |
+------------+
|       NULL |
+------------+
1 row in set (0.00 sec)

mysql> call p1('hi');
+------------+
| @randomvar |
+------------+
|          2 |
+------------+
1 row in set (0.00 sec)

MySQL:

mysql>  CREATE PROCEDURE p1(x VARCHAR(20)) BEGIN SET @randomvar = (SELECT LENGTH(x)); SELECT @randomvar; END;#
mysql> delimiter ;
mysql> call p1('hi');
+------------+
| @randomvar |
+------------+
|          2 |
+------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

mysql> call p1('hi');
+------------+
| @randomvar |
+------------+
|          2 |
+------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)