hi,
the system allow empty search, in future we will add a option to allow or not this. we can't add this in next release because it will be released tomorrow.

Hi Luiza,
to exclude Super User you can put this in SQL Custom Where

user_id NOT IN (456)

replace 456 with Super User ID

to exclude All Super Users (Administrators) you can put this in SQL Custom Where

group_id NOT IN (8)

8 is a ID of Super Users usergroup in most installations of Joomla.

docs at https://www.easy-profile.com/docs/69-sql-custom-where-list-and-module.html