In admin/bloglevelupgrade_entries.php on line 91 the attribute 'intro' for the discussion object is set, this used to be named message. If this renaming is supposed to occur then the forum_add_discussion method in forum/lib.php needs updating to reflect this.

Debug info: Column 'message' cannot be null
INSERT INTO mdl_forum_posts (discussion,parent,userid,created,modified,mailed,subject,message,messageformat,messagetrust,mailnow) VALUES(?,?,?,?,?,?,?,?,?,?,?)
[array (
0 => 0,
1 => 0,
2 => '3',
3 => 1300434064,
4 => 1300434064,
5 => 0,
6 => 'Background',
7 => NULL,
8 => '0',
9 => 0,
10 => 0,
)]
Stack trace:

• line 394 of /lib/dml/moodle_database.php: dml_write_exception thrown
• line 874 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
• line 916 of /lib/dml/mysqli_native_moodle_database.php: call to mysqli_native_moodle_database->insert_record_raw()
• line 4121 of /mod/forum/lib.php: call to mysqli_native_moodle_database->insert_record()
• line 102 of /admin/bloglevelupgrade.php: call to forum_add_discussion()
• line 70 of /admin/bloglevelupgrade.php: call to bloglevelupgrade_entries()