How to unset DNS servers with networksetup command?

Hi.

I set DNS server setting at terminal with networksetup command.

shell> sudo networksetup -setdnsservers "Wi-Fi" 127.0.0.1

How to unset DNS servers with networksetup command?

Such as...

shell> sudo networksetup -setdnsservers "Wi-Fi" // not working!

I want to switch quickly and easily when connect to DNS overriding free wi-fi spots.

Thanks.