Coding error while generating data use admin tool 'Generator'

Replication steps:

1. Open '/admin/tool/generator'.
2. Create a few courses including forum module.
3. Leave default values for forum options
4. Click the 'Generate Data' button.
5. And you will find the following error:

   Error writing to database

   More information about this error

   Debug info: Column 'message' cannot be null

   INSERT INTO m24_forum_posts (discussion,parent,userid,created,modified,mailed,subject,message,messageformat,messagetrust,mailnow) VALUES(?,?,?,?,?,?,?,?,?,?,?)

   [array (

   0 => 0,

   1 => 0,

   2 => '7747',

   3 => 1373424007,

   4 => 1373424007,

   5 => 0,

   6 => 'Test discussion',

   7 => NULL,

   8 => 1,

   9 => 0,

   10 => 0,

   )]

   Error code: dmlwriteexception