Environment: a new LDAP entry try to authenticate for the first time in Moodle and still there isn't a record in mdl_user table.

When this new user try to authenticate, authenticate_user_login function is called. If the credentials are correct, it search the correct record in mdl_user table without success and it calls create_user_record.
This function try to create a new record, but this is the error message:

Field 'city' doesn't have a default value

INSERT INTO mdl_user ( AUTH, CONFIRMED, MNETHOSTID, USERNAME, FIRSTNAME, LASTNAME, LANG, LASTIP, TIMEMODIFIED ) VALUES ( 'ldap', 1, 1, 'd.eliseo', 'Donato', 'Eliseo', 'it_utf8', '10.250.1.21', 1229596730 )
line 1425 of lib/dmllib.php: call to debugging()
line 2603 of lib/moodlelib.php: call to insert_record()
line 2787 of lib/moodlelib.php: call to create_user_record()
line 126 of login/form.php: call to authenticate_user_login()

infact City Field is a nonull param as you see in cvs:/lib/db/install.xml without default value

Solution: adding something like:
$newuser->city = '';
in create_user_record function in cvs:/lib/moodlelib.php