Bug #44481 cast/convert function not working correctly with NULL value

Description:
When I'm casting NULL value as signed integer or unsigned integer i get NULL.

mysql> select cast(NULL as signed integer);
+------------------------------+
| cast(NULL as signed integer) |
+------------------------------+
|                         NULL |
+------------------------------+
1 row in set (0.00 sec)

mysql> select cast(NULL + 1 as signed integer);
+----------------------------------+
| cast(NULL + 1 as signed integer) |
+----------------------------------+
|                             NULL |
+----------------------------------+
1 row in set (0.00 sec)

mysql> select convert(NULL + 1 , signed integer);
+------------------------------------+
| convert(NULL + 1 , signed integer) |
+------------------------------------+
|                               NULL |
+------------------------------------+
1 row in set (0.00 sec)

mysql> select convert(NULL , signed integer);
+--------------------------------+
| convert(NULL , signed integer) |
+--------------------------------+
|                           NULL |
+--------------------------------+
1 row in set (0.00 sec)

mysql> select convert(NULL , signed);
+------------------------+
| convert(NULl , signed) |
+------------------------+
|                   NULL |
+------------------------+
1 row in set (0.00 sec)
 

How to repeat:
mysql> select convert(NULL , signed);
mysql> select convert(NULL , signed integer);
mysql> select convert(NULL + 1 , signed integer);
mysql> select cast(NULL + 1 as signed integer);
mysql> select cast(NULL as signed integer);

Why do you think there is a bug here? NULL is NULL, whatever type it is. And if NULL is an operand in expression, the result is usually NULL. This is expected.

Maybe I'm thinking wrong way but for example i want to get something like that:

SELECT CAST(MAX(field) AS UNSIGNED) + 1 AS next_number FROM table; 

For empty table I'm expecting to get 1 as next_number. Maybe my thinking is wrong. I read this earlier today: http://bugs.mysql.com/bug.php?id=2219

Current behavior is intended. You can use functions in your expression to check for NULL and return the result you need for this case. Check http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html#function_ifnull.

Ok, my mistake. Didn't know it is intended. Thank for link :) Regards