Warnig message is displayed when loggin in via ssh:

"Warning: your password will expire in 0 days."

By the "man 5 shadow" documentation:

       date of last password change
           The date of the last password change, expressed as the number of days since Jan 1, 1970 00:00 UTC.

           The value 0 has a special meaning, which is that the user should change her password the next time she will log in
           the system.

           An empty field means that password aging features are disabled.

However, the third field in the /etc/shadow file is empty for the user (actually it is the root account).