Trying to use scanner in java to read just a stroke of the return key as an input?

I am making a program that will read user input and determine with an if else loop what to do. If the user hits just enter and doesn't type anything else in, I want to loop something through the if. If anything else is typed as an input, the program should exit back to a different menu. Here is what I have so far:

Scanner scnr = new Scanner(System.in);
String choice;
choice = scnr.next();
if (choice.equals("")){ ...
}
else {...
}

When I run through it, just pressing enter does affect anything, it just makes advances to the next line in the console. However, when I type something in, the error part that sends it to the menu when anything else is typed in works just fine. I'm thinking I have to use something besides scnr.next(); but I don't know what that would be.

This is for an entry level class, and it requires that we use the scanner utility and not something more advanced. Thanks in advance.