Provide a consistent hint when an user registers with a password with only whitespaces

STEPS TO REPRODUCE

1. On Registration page, register an user
2. Fill the required fields
3. Insert 6 empty spaces in 'Password' and 'Confirm Password' fields

EXPECTED RESULTS

A hint is displayed below the 'Password' and 'Confirm Password' fields informing the user that the password cannot be empty (warning like 'Password cannot contain only empty spaces').

 ACTUAL RESULTS

The hint displays: 'Ok', even if there are only empty (6) spaces inserted. After clicking 'Register', a warning message is displayed right below the page's title:

Passwords are different or password is empty.

On XWiki 11.9 however, the warning is incomplete (which did not reproduce on XWiki 11.3.5 or 11.8.1):

are different or password is empty.