Handler Class Crashing after removing object

Question

That was probably a very confusing title, but I'm pretty confused. I am making a game, and there are explosions. I just ran into this one stupid problem. Here's my code for the explosions (without the package and imports):

public class LBExplosion extends GameObject{
private int tick;
private int startSize,endSize,size;
Handler handler;
public LBExplosion(float x, float y, ID id, int startSize, int endSize, Handler handler) {
    super(x, y, id);
    // TODO Auto-generated constructor stub
    this.startSize = startSize;
    this.endSize = endSize;
    size = startSize;
}

@Override
public void tick() {
    // TODO Auto-generated method stub
    tick++;
    size++;
    if (size >= endSize) {
        this.handler.removeObject(this); //here
    }
}

@Override
public void render(Graphics g) {
    // TODO Auto-generated method stub
    if (tick % 2 == 0) {
        g.setColor(Color.white);
    } else if (tick % 2 == 1) {
        g.setColor(Color.red);
    }
    g.fillRect((int) x - size/2, (int) y - size/2, size, size);
}

@Override
public Rectangle getBounds() {
    // TODO Auto-generated method stub
    return null;
}

}

And it errors when I try to remove it (at line 25).

Here's the code for the handler class (without the package and imports):

public class Handler {
LinkedList <GameObject> objList = new LinkedList <GameObject>();

public void tick() {
    for (int i = 0; i < objList.size(); i++) {
        GameObject tempObject = objList.get(i);
        tempObject.tick();
    }
}
public void render(Graphics g) {
    for (int i = 0; i < objList.size(); i++) {
        GameObject tempObject = objList.get(i);
        tempObject.render(g);
    }
}

public void addObject(GameObject object) {
    objList.add(object);
}
public void removeObject(GameObject object) {
    objList.remove(object);
}
public void removeAllEnemies() {
    for (int i = 0; i < objList.size(); i++) {

    }
}

} And here's the constructor for the game class (where it's spawned):

public Game() {
    handler = new Handler();
    hud = new HUD();
    spawner = new Spawner(handler);

    this.addKeyListener(new KeyInput(handler));
    new Window(WIDTH,HEIGHT,"Game", this);

    handler.addObject(new Player (16, 16, ID.Player,hud,handler));
    handler.addObject(new LBExplosion (300, 316, ID.LBExplosion,0,64,handler));

}

It gives me this error:

Exception in thread "Thread-2" java.lang.NullPointerException
at com.wave.noah.two.p.a.c.k.a.g.e.something.main.LBExplosion.tick(LBExplosion.java:26)
at com.wave.noah.two.p.a.c.k.a.g.e.something.main.Handler.tick(Handler.java:12)
at com.wave.noah.two.p.a.c.k.a.g.e.something.main.Game.tick(Game.java:80)
at com.wave.noah.two.p.a.c.k.a.g.e.something.main.Game.run(Game.java:62)
at java.lang.Thread.run(Unknown Source)

Don't mind the long package name.

How do I fix this unexpected error?