java.util.scanner - Java scanner test for empty line

I'm using Scanner to read 3 lines of input, the first two are strings and the last one is int.
I'm having an issue when the first line is empty and I don't know how to get around it. I have to do this:

String operation = sc.nextLine();
String line = sc.nextLine();

int index = sc.nextInt();
encrypt(operation,line,index);

But when the first line is empty I get an error message.
I tried the following to force a loop until I get a non empty next line but it does not work either:

        while(sc.nextLine().isEmpty){
        operation = sc.nextLine();}

Anybody has a hint please ?

Answer

A loop should work, though you must actually call the isEmpty method and scan only once per iteration

String operation = "";
do {
    operation = sc.nextLine();
} while(operation.isEmpty());

You could also use sc.hasNextLine() to check if anything is there