Running sudo when user has blank password?
sudo on macOS requires the account to have a password:
https://support.apple.com/en-us/HT202035
Therefore it is not possible to just press ENTER to continue at the prompt, like you would expect from some other systems.
This behaviour is enforced through a configuration of the PAM subsystem. You can change the settings for that in /etc/pam.d, where you have a sudo file that setups the authentication requirements for the sudo command.
WARNING: Changing the contents of the files in /etc/pam.d incorrectly can deny you from logging to your system at all. Only make changes if you know what you're doing, you have a backup - and you feel confident in booting in Recovery mode to undo your changes if it should fail.