[3.9.16-dev] com_users. Save options => Error "Field required: Domain Name"

[ReLater]

Steps to reproduce the issue

• New installation of nightly build 3.9.16-dev
• Opened Users: Options
• Activated: Allow User Registration
• Clicked Save

Expected result

• Options saved

Actual result

System information (as much as possible)

Setting	Value
PHP Built On	Linux dd46134 4.15.0-76-generic #86~16.04.1-Ubuntu SMP Mon Jan 20 11:02:50 UTC 2020 x86_64
Database Type	mysql
Database Version	5.7.28-nmm1-log
Database Collation	utf8_general_ci
Database Connection Collation	utf8mb4_general_ci
PHP Version	7.4.2
Web Server	Apache
WebServer to PHP Interface	fpm-fcgi
Joomla! Version	Joomla! 3.9.16-dev Development [ Amani ] 27-January-2020 17:50 GMT
Joomla! Platform Version	Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
User Agent	Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:73.0) Gecko/20100101 Firefox/73.0

Additional comments

• When I go in tabulator Email Domain Options and create a dummy row like
  

I can save the options

[Quy]

See PR #27999 awaiting to be merged.