Yea, sorry. MySQL can show NULL as the default value, when in fact it 
is not really NULL.

http://bugs.mysql.com/bug.php?id=34198

I think the point is that there *is* no default value for that field. 
Not sure where the '0' came from.

Worked fine after fixing this.

Or no default value at all, I see.

Where ever this comes from, this is a NOT NULL field, so it must have 
a default value different than NULL.

In fact, most of those '0' default values are shown as NULL for me.

I'm not sure how/why there is a default value of '0' for that field. 
The install I haven't migrated yet shows 'NULL' there, as does the 
install I have run a fresh install on.

Of the current nag_shares table? (this is not a fresh install)

+-----------------+--------------+------+-----+---------+-------+
| Field           | Type         | Null | Key | Default | Extra |
+-----------------+--------------+------+-----+---------+-------+
| share_id        | int(11)      | NO   | PRI | 0       |       |
| share_name      | varchar(255) | NO   | MUL |         |       |
| share_owner     | varchar(255) | YES  | MUL | NULL    |       |
| share_flags     | smallint(6)  | NO   |     | 0       |       |
| perm_creator    | smallint(6)  | NO   | MUL | 0       |       |
| perm_default    | smallint(6)  | NO   | MUL | 0       |       |
| perm_guest      | smallint(6)  | NO   | MUL | 0       |       |
| attribute_name  | varchar(255) | NO   |     |         |       |
| attribute_desc  | varchar(255) | YES  |     | NULL    |       |
| attribute_color | varchar(7)   | YES  |     | NULL    |       |
+-----------------+--------------+------+-----+---------+-------+

I'm not seeing this with either a new install or migration of existing 
table. I don't see where the share_id field would even have a default 
value either.  What does DESCRIBE show?

2010-11-04T12:45:22+00:00 INFO: -- changeColumn(nag_shares, share_id, 
integer, array(null => false, autoincrement => true))
SQLSTATE[42000]: Syntax error or access violation: 1067 Invalid 
default value for 'share_id'