[turba] There was an error adding the new contact

[yahsuan at Lab400-51.cc.ntu.edu.tw]

my horde app version is:
horde                     4.0.1   stable
imp                       5.0.1   stable
ingo                      2.0.1   stable
turba                     3.0.1   stable

and my php version is PHP 5.3.3

When I want to new contact in my address books, if I don't filed
[other]->[Category],
there will be error:

There was an error adding the new contact. Contact your system
administrator for further help.

and I check my log file, the error message is:

..

          object_cellphone = '', object_fax = '', object_pager = '',
          object_title = '', object_role = '', object_company = '',
object_logo
          = NULL, object_logotype = NULL, object_category =, object_notes =
'',
          object_url = '', object_freebusyurl = '', object_pgppublickey =
'',
          object_smimepublickey = '' WHERE object_id =
'j5AiXrd-V21Nt8MV7d4yu_A' [pid 11231 on line 792 of
"/usr/share/php/Horde/Db/Adapter/Base.php"]
2011-04-27T15:18:20+08:00 ERR: HORDE [turba] SQLSTATE[42601]: Syntax error:
7 ??:  ?"????"???? ,
? 1: ...= NULL, object_logotype = NULL, object_category = , object_n..
                                                                          
              ^ [pid 11231 on line 505 of
"/var/www/mail/horde-4/turba/lib/Driver/Sql.php"]

It seems that the object_category field didn't have the default value like
other fields.('' or NULL)

How can I fix it?
Thanks in advance.