Why can't I initialize an object in app base?

I am unable to initialize or store an object in a class that extends the Application AppBase, Is this expected?

With the below implementation I get a "Illegal Access(AOB)" error

*This is for a DataField

class MySensorImplementation() {
    function initialize() {
        // Stuff
    }
}

class MyApp extends App.AppBase {
   var sensor;

	function initialize() {
		AppBase.initialize();
		
		sensor = new MySensorImplementation();
	}

	// onStart() is called on application start up
	function onStart(state) {
		AppBase.onStart(state);
	}

	// onStop() is called when your application is exiting
	function onStop(state) {
		AppBase.onStop(state);
		sensor.close() // <-- this is why i want sensor to be initialized here
	}

	// Return the initial view of your application here
	function getInitialView() {
		return [
			new myView(sensor) <-- I want to pass sensor in here
		];
	}
}