Thank you.

I changed definition directly in my DB.

I'm using Horde/Turba for a lot of years, the default was changed, may be.

Correct, allowing nulls is the default behavior.

I'm sorry, it's look like bug.

I have updated DB and I haven't good definition.

I found definition for "object_members" only in file 
"turba/migration/1_turba_base_tables.php"

The definition is:

             $t->column('object_members', 'text');

There is no information about NULL like in other columns: "'null' => false"

So it's not look like good, I hope.

The tables are created using migrations. See turba/migration directory.

As this is not a bug, please use the mailing list for further support.

http://www.horde.org/mail/ contains a list of all available mailing lists.

OK, may be I have old table definition.
DB schema look like OK I have "SQL DB schema is ready" in horde settings

Where can I find table definition for Turba?

I can't reproduce this. The default turba migrations create a nullable 
column for object_members.

I setup new Exchange/Horde account on Android phone, than create new 
contact on the phone and run contacts synchronization.

I'm sorry, I don't known where is the SQL command created, but it's look like:

UPDATE `turba_objects` SET `object_members` = NULL

It's wrong because for object_members NULL value is disabled.

I hope, there is two solutions:
- change object_members definition in DB
- change SQL command to not use NULL, default value for object_members is ""

It would be helpful to know what you were doing to trigger this. I.e., 
how to reproduce this...

I find problem with ActiveSync and Turba in SQL.

It's look like bad column definition or SQL in command.

The Error:

Sep 26 10:41:39 ecn4 HORDE: [turba] SQL QUERY FAILED: Column 
'object_members' cannot be null  #012#011UPDATE `turba_objects` SET 
`owner_id` = '***', `object_type`#012#011  = 'Object', 
`object_members` = NULL, `object_uid` =#012#011   
'20180926103222.dVI3oddh6Jo9jwTvFXEtJt4@webmail.ecn.cz',#012#011   
`object_firstname` = 'J', `object_lastname` = 'webmail',#012#011   
`object_middlenames` = '', `object_nameprefix` = '',#012#011   
`object_namesuffix` = '', `object_alias` = '', 
`object_yomifirstname`#012#011  = '', `object_yomilastname` = '', 
`object_bday` = '',#012#011  `object_anniversary` = '', 
`object_spouse` = '', `object_photo` = '',#012#011  `object_phototype` 
= NULL, `object_homestreet` = '', `object_homepob`#012#011  = NULL, 
`object_homecity` = '', `object_homeprovince` = '',#012#011   
`object_homepostalcode` = '', `object_homecountry` = '',#012#011   
`object_workstreet` = '', `object_workpob` = NULL, `object_workcity` 
=#012#011  '', `object_workprovince` = '', `object_workpostalcode` = 
'',#012#011  `object_workcountry` = '', `object_otherstreet` = 
'',#012#011  `object_otherpob` = NULL, `object_othercity` = 
'',#012#011  `object_otherprovince` = '', `object_otherpostalcode` = 
'',#012#011  `object_othercountry` = '', `object_department` = '', 
`object_manager`#012#011  = '', `object_assistant` = '', `object_tz` = 
NULL, `object_email` =#012#011  '', `object_homephone` = '', 
`object_homephone2` = '',#012#011  `object_homefax` = '', 
`object_workphone` = '', `object_workphone2` =#012#011  '', 
`object_cellphone` = '111 111 111, `object_carphone` = '',#012#011   
`object_radiophone` = '', `object_companyphone` = '',#012#011   
`object_assistantphone` = '', `object_fax` = '', `object_pager` = 
'',#012#011  `object_title` = '', `object_role` = NULL, 
`object_company` = 'ecn#012#011  studio', `object_logo` = NULL, 
`object_logotype` = NULL,#012#011  `object_notes` = NULL, `object_url` 
= '', `object_freebusyurl` = NULL,#012#011  `object_pgppublickey` = 
NULL, `object_smimepublickey` = NULL,#012#011  `object_imaddress` = 
'', `object_imaddress2` = '', `object_imaddress3`#012#011  = '', 
`object_homeemail` = '', `object_workemail` = '' WHERE 
object_id#012#011  = '4g8JGm81OB90NWlH2qjv8ec' [pid 14166 on line 318 
of "/usr/share/pear/Horde/Db/Adapter/Mysqli.php"]