/**** 
* Classes
****/ 
// Bullet class
var Bullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.attachAsset('bullet', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = -5;
	self.update = function () {
		self.y += self.speed;
	};
});
// Space DOT class
var SpaceDOT = Container.expand(function () {
	var self = Container.call(this);
	var dotGraphics = self.attachAsset('spaceDOT', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = 2;
	self.health = 3;
	self.healthBar = self.attachAsset('healthBar', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.healthBar.scaleX = self.health / 3;
	self.update = function () {
		self.y += self.speed;
		self.healthBar.scaleX = self.health / 3;
		if (self.y > 2732) {
			self.y = -self.height;
		}
	};
});
// Space Pirate class
var SpacePirate = Container.expand(function () {
	var self = Container.call(this);
	var pirateGraphics = self.attachAsset('spacePirate', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = 3;
	self.update = function () {
		self.y += self.speed;
		if (self.y > 2732) {
			self.y = -self.height;
		}
	};
});
//<Assets used in the game will automatically appear here>
// Truck class
var Truck = Container.expand(function () {
	var self = Container.call(this);
	var truckGraphics = self.attachAsset('truck', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = 5;
	self.update = function () {
		// Truck movement logic
		if (LK.ticks % 30 == 0) {
			var newBullet = new Bullet();
			newBullet.x = self.x;
			newBullet.y = self.y;
			bullets.push(newBullet);
			game.addChild(newBullet);
		}
	};
	self.move = function (x, y, obj) {
		self.x = x;
		self.y = y;
	};
});

/**** 
* Initialize Game
****/ 
var game = new LK.Game({
	backgroundColor: 0x000000 //Init game with black background 
});

/**** 
* Game Code
****/ 
// Initialize bullets
var bullets = [];
// Initialize truck
var truck = game.addChild(new Truck());
truck.x = 2048 / 2;
truck.y = 2732 - 200;
// Initialize space pirates
var spacePirates = [];
var currentWave = 1;
for (var i = 0; i < 3; i++) {
	var pirate = new SpacePirate();
	pirate.x = Math.random() * 2048;
	pirate.y = Math.random() * -2732;
	spacePirates.push(pirate);
	game.addChild(pirate);
}
// Initialize space DOTs
var spaceDOTs = [];
for (var i = 0; i < 5; i++) {
	var dot = new SpaceDOT();
	dot.x = Math.random() * 2048;
	dot.y = Math.random() * -2732;
	spaceDOTs.push(dot);
	game.addChild(dot);
}
// Handle truck movement
game.move = function (x, y, obj) {
	truck.x = x;
	truck.y = y;
};
// Update game logic
game.update = function () {
	// Update game logic
	// Update bullets
	for (var i = bullets.length - 1; i >= 0; i--) {
		bullets[i].update();
		// Check collision with space pirates
		for (var j = spacePirates.length - 1; j >= 0; j--) {
			if (bullets[i].intersects(spacePirates[j])) {
				game.removeChild(bullets[i]);
				game.removeChild(spacePirates[j]);
				bullets.splice(i, 1);
				spacePirates.splice(j, 1);
				break;
			}
		}
		// Check collision with spaceDOTs
		for (var j = spaceDOTs.length - 1; j >= 0; j--) {
			if (bullets[i] && bullets[i].intersects(spaceDOTs[j])) {
				game.removeChild(bullets[i]);
				bullets.splice(i, 1);
				spaceDOTs[j].health -= 1;
				if (spaceDOTs[j].health <= 0) {
					game.removeChild(spaceDOTs[j]);
					spaceDOTs.splice(j, 1);
				}
				break;
			}
		}
	}
	for (var i = 0; i < spacePirates.length; i++) {
		spacePirates[i].update();
		if (truck.intersects(spacePirates[i])) {
			LK.effects.flashScreen(0xff0000, 1000);
			LK.showGameOver();
		}
		// If all space pirates are defeated, increase the wave and the number of space pirates
		if (spacePirates.length == 0) {
			currentWave++;
			for (var j = 0; j < currentWave * 2 + 1; j++) {
				var pirate = new SpacePirate();
				pirate.x = Math.random() * 2048;
				pirate.y = Math.random() * -2732;
				spacePirates.push(pirate);
				game.addChild(pirate);
			}
		}
	}
	// Update space DOTs
	for (var i = 0; i < spaceDOTs.length; i++) {
		spaceDOTs[i].update();
		if (truck.intersects(spaceDOTs[i])) {
			LK.effects.flashScreen(0xff0000, 1000);
			LK.showGameOver();
		}
	}
};

===================================================================
--- original.js
+++ change.js
@@ -132,9 +132,9 @@
 			}
 		}
 		// Check collision with spaceDOTs
 		for (var j = spaceDOTs.length - 1; j >= 0; j--) {
-			if (bullets[i].intersects(spaceDOTs[j])) {
+			if (bullets[i] && bullets[i].intersects(spaceDOTs[j])) {
 				game.removeChild(bullets[i]);
 				bullets.splice(i, 1);
 				spaceDOTs[j].health -= 1;
 				if (spaceDOTs[j].health <= 0) {