Odd returning of ArrayList#size()

I am trying to get a random ArrayList in a HashMap, and when I look at all the ArrayLists in the HashMap the size of everything is 2 as it should.

The problem occurs when I try to add an ArrayList from the Hashmap into another. It then returns the size as 0 even though the size of all lists in the HashMap are 2. Does anyone see why?

        for(Point p : defensePossibilities.keySet())
            System.out.println(defensePossibilities.get(p).size());

        ArrayList<Point> points = new ArrayList<>();
        while(points == null) {
            try {
                int random = rnd.nextInt(defensePossibilities.size());
                points.addAll(
                        defensePossibilities.get(random));
            } catch(Exception e) {}
        }
        System.out.println("PointsSize: " + points.size());

        int piece2 = rnd.nextInt(
                        points.size());

This is what it returns in the stacktrace

2
2
2
2
2
2
2
2
PointsSize: 0
Exception in thread "Thread-0" java.lang.IllegalArgumentException: bound must be positive
    at java.util.Random.nextInt(Unknown Source)
    at me.xthegamerplayz.FirstGame.board.White_AI.move(White_AI.java:95)
    at me.xthegamerplayz.FirstGame.board.ChessBoard.tick(ChessBoard.java:29)
    at me.xthegamerplayz.FirstGame.board.ChessBoard.<init>(ChessBoard.java:21)
    at me.xthegamerplayz.FirstGame.Game.render(Game.java:124)
    at me.xthegamerplayz.FirstGame.Game.run(Game.java:70)
    at java.lang.Thread.run(Unknown Source)

Line 95 is

int piece2 = rnd.nextInt(

Why is the size of points 0 if all the ArrayLists in the HashMap are at the size of 2.