Steps to reproduce:

1. Install zabbix 4.0.?, with PostgreSQL 10.8 database and ElaticSearch(all data backend)
2. Enabled LDAP auth.
3. Created few ldap users
4. Server udateed to 4.2.1
5. Creating new user without password

Result:
Cannot add user

• Incorrect value for field "passwd": cannot be empty.
  Expected:
  I created user by insert to database, error not changed.

Users who been create before update have no erros.