public static String returnValue(CtBehavior method) throws NotFoundException {

        String returnValue = "";
        if (methodReturnsValue(method)) {
            returnValue = " returns: \" + $_ + \".";
        }
        return returnValue;
    }
Create a javassist source snippet which either is empty (for anything
which does not return a value) or an explanatory text around the $_
javassist return value variable.

@param method
           descriptor of method
@return source snippet
@throws NotFoundException
slf4j-ext/src/main/java/org/slf4j/instrumentation/JavassistHelper.java