I would like visudo to verify if an "included file" is empty before quitting.

When sudoers has "include" statements and you edit the "included file" visudo does not verify if you left the file empty. So, whenever try to use "sudo" you get 

'sudo ls
sudo: /etc/sudo.file is zero length
>>> /etc/sudoers: /etc/sudo.file near line 48 <<<
sudo: parse error in /etc/sudoers near line 48
sudo: no valid sudoers sources found, quitting'

and

'sudo visudo
sudo: /etc/sudo.file is zero length
>>> /etc/sudoers: /etc/sudo.file near line 48 <<<
sudo: parse error in /etc/sudoers near line 48
sudo: no valid sudoers sources found, quitting'

At that moment sudo is useless.