Adding Position.enableLocationEvents to new app

Hi there,

Apologies, I am new to Garmin app development and still am learning. 

I just had a question about adding location events tracking to the base app that is created when you open a new application project. 

Why does adding Position.enableLocationEvents(Position.LOCATION_CONTINUOUS, method(:onPosition)); cause the app not to start, as below?

Thank you

import Toybox.Application;
import Toybox.Lang;
import Toybox.WatchUi;
import Toybox.Position;

class myIntervalAppApp extends Application.AppBase {

    function initialize() {
        AppBase.initialize();
    }

    // onStart() is called on application start up
    function onStart(state as Dictionary?) as Void {
        Position.enableLocationEvents(Position.LOCATION_CONTINUOUS, method(:onPosition)); // HERE
    }

    // onStop() is called when your application is exiting
    function onStop(state as Dictionary?) as Void {
    }

    // Return the initial view of your application here
    function getInitialView() as Array<Views or InputDelegates>? {
        return [ new myIntervalAppView(), new myIntervalAppDelegate() ] as Array<Views or InputDelegates>;
    }

    public function onPosition(info as Info) as Void {
    }

}

function getApp() as myIntervalAppApp {
    return Application.getApp() as myIntervalAppApp;
}