It seems nothing is wrong in  the code but somehow I am getting " java.lang.IndexOutofBoundsException Index: 0,Size: 0 " error

Any suggestion

error  log:

2. import SimpleOpenNI.*;
3. import org.processing.wiki.triangulate.*;
4. ArrayList triangles = new ArrayList();
5. ArrayList points = new ArrayList();
6. SimpleOpenNI  kinect;
7. int userID;
8. Boolean tracking=false;
9. int[] userMap = null;
10. void setup() {
11.   size(640, 480, P3D);
12.   kinect = new SimpleOpenNI(this);
13.   kinect.enableDepth();
14.   kinect.enableUser(SimpleOpenNI.SKEL_PROFILE_NONE);
15. }
16. 
    
17. void draw() {
18.   background(0);
19.   kinect.update();
20.   if (kinect.getNumberOfUsers()>0) {
21.     userMap = kinect.getUsersPixels(SimpleOpenNI.USERS_ALL);  // find out which pixels have users in them// populate  the pixels array
22.   } // from the sketch's current contents
23.   loadPixels();
24.   for (int x=0; x<width; x++) {
25.     for (int y=0; y<height; y++) {
26.       int index = x + y * width;
27.       if ( userMap!=null &&  userMap[index] > 0) {
28.         points.add(new PVector(x, y));
29.         pixels[index] = color(255, 0, 0);
30.       }
31.     }
32.   }
33.   // display the changed pixel array
34.   updatePixels();
35. 
    
36.   //-------------------------------
37.   triangles = Triangulate.triangulate(points);
38.   //-------------------------------
39.   stroke(0, 40);
40.   fill(255, 40);
41.   beginShape(TRIANGLES);
42.   for (int i = 0; i < triangles.size(); i++) {
43.     Triangle t = (Triangle)triangles.get(i);
44.     vertex(t.p1.x, t.p1.y);
45.     vertex(t.p2.x, t.p2.y);
46.     vertex(t.p3.x, t.p3.y);
47.   }
48.   endShape();
49.   //-------------------------------
50. }
51. void onNewUser(int uID) {
52.   userID = uID;
53.   tracking = true;
54.   println("tracking");
55. }