Why is line #29 is causing a NullPointerException?

Question

I am creating an atari breakout game in processing and I'm trying to figure out the collision detection that allows the ball to bounce off the controller. The commented out lines (along with the hitController function) is supposed to be the method for this and the program runs fine without the commented lines but with them, it causes a NullPointerException. Any suggestions?

class Ball {
  float rad = 15;
  float xpos, ypos;
  float xspeed = 2.8;
  float yspeed = 2.2;
  float xdir = 1;
  float ydir = 1;
  Controller controller;

  Ball(){
    noStroke();
    ellipseMode(RADIUS);
    xpos = width/2;
    ypos = height/2;

  }

  void move(){
    xpos = xpos + (xspeed * xdir);
    ypos = ypos + (yspeed * ydir);

    if(xpos > width - rad || xpos < rad){
      xdir *= -1;
    }
    if(ypos > height - rad || ypos < rad){
      ydir *= -1;
    }
    //boolean hit = hitController(xpos, ypos, rad, controller.getY());
    //if(hit){
      //xdir *= -1;
      //ydir *= -1;
    //}
  }

   void display(){
    ellipse(xpos, ypos, rad, rad);
    }

    boolean hitController(float cx, float cy, float rad, float ry){
      float testX = cx;
      float testY = cy;
      if(cy < ry){
        testY = ry;
      }
      float distX = cx - testX;
      float distY = cy - testY;
      float distance = sqrt((distX * distX)+(distY * distY));

      if(distance <= rad){
        return true;
      } else {
        return false;
      }
    }

  }

edit: I have included the controller class below as well.

class Controller {
  int cwidth;
  int cheight;
  color c;
  float x, y;

  Controller() {
    cwidth = 155;
    cheight = 15;
    c = color(50,10,10,150);
    x = 0;
    y = 0;
  }

  void setLocation(int x, int y) {
    this.x = x;
    this.y = y;
  }


  void display() {
    x = constrain(mouseX, 70, 640 );
    y = constrain(mouseY, 480, 480);

    rectMode(CENTER);
    fill(c);
    rect(x, y, cwidth, cheight);

  }

  float getX() {
    return x;
  }

  float getY() {
    return y;
  } 
}