Attempt to write to null array error

I am trying to create an app that scrambles a picture. It works great in Java mode but I get the following error in Android mode.

FATAL EXCEPTION: Animation Thread Process: processing.test.pic_sensoring, PID: 7254 java.lang.NullPointerException: Attempt to write to null array at processing.test.pic_sensoring.pic_sensoring.setup(pic_sensoring.java:49) at processing.core.PApplet.handleDraw(Unknown Source) at processing.core.PGraphicsAndroid2D.requestDraw(Unknown Source) at processing.core.PApplet.run(Unknown Source) at java.lang.Thread.run(Thread.java:761)

My abstracted Code:

PImage img;

void setup(){

  size (200,200);
  img = loadImage("KoalaBear.jpg");
  loadPixels();
  img.loadPixels();

int half1 = img.pixels.length/2;
for(int x = 0 ; x < img.pixels.length/2; x++){
  int a = 0;
  if (a != 199){
  a++;
  }else{
  a = 0;
  }

  int y = x/200 + a/200;

if ((x % 10 < 5) &&( y % 10 < 5)) {
        img.pixels[x]  = color(127);  // White
      }//if block

}//for loop



 img.updatePixels();

}

void draw(){
  image(img3,0,0);
}//draw