Question: I need to allow saving null as integer value on mysql server, how can I do this?

Answer: 
Assuming your question is about the "Incorrect integer value" error message...

```
mysql> CREATE TABLE `foo` (
    ->  `foo_id` INT(10) NOT NULL AUTO_INCREMENT,
    ->  `foo_size` INT(10) NOT NULL DEFAULT '0',
    ->  PRIMARY KEY (`foo_id`)
    -> ) ENGINE=MyISAM;
Query OK, 0 rows affected (0.05 sec)

mysql> INSERT INTO foo (foo_size) VALUES ('');
ERROR 1366 (HY000): Incorrect integer value: '' for column 'foo_size' at row 1

```

... that means that your server is running in strict mode (which is actually good). You can disable it:

```
mysql> SET @@session.sql_mode='';
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO foo (foo_size) VALUES ('');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> SHOW WARNINGS;
+---------+------+------------------------------------------------------------+
| Level   | Code | Message                                                    |
+---------+------+------------------------------------------------------------+
| Warning | 1366 | Incorrect integer value: '' for column 'foo_size' at row 1 |
+---------+------+------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT * FROM foo;
+--------+----------+
| foo_id | foo_size |
+--------+----------+
|      1 |        0 |
+--------+----------+
1 row in set (0.00 sec)

```

... and your error will be downgraded to warning.
Set the field to not null and set its default to zero:

```
CREATE TABLE `t` (
    `foo` BIGINT NOT NULL DEFAULT 0
);

```

Value of `foo` will be zero if you send it NULL.