Object reference not set to an instance of an Object

using UnityEngine; using System.Collections;

public class PlayerController : MonoBehaviour {

 public GameObject playerObject;


 public float walkSpeed = 2;
 public float runSpeed = 6;
 public float gravity = -12;
 public float jumpHeight = 1;
 [Range(0,1)]
 public float airControlPercent;

 public float turnSmoothTime = 0.2f;
 float turnSmoothVelocity;

 public float speedSmoothTime = 0.1f;
 float speedSmoothVelocity;
 float currentSpeed;
 float velocityY;

 Animator animator;
 Transform cameraT;
 CharacterController controller;

 void Start () {
     animator = GetComponent<Animator> ();
     cameraT = Camera.main.transform;
     controller = GetComponent<CharacterController> ();
 }

 void Update () {
     // input
     Vector2 input = new Vector2 (Input.GetAxisRaw ("Horizontal"), Input.GetAxisRaw ("Vertical"));
     Vector2 inputDir = input.normalized;
     bool running = Input.GetKey (KeyCode.LeftShift);

     Move (inputDir, running);

     if (Input.GetKeyDown (KeyCode.Space)) {
         Jump ();
     }
     // animator
     float animationSpeedPercent = ((running) ? currentSpeed / runSpeed : currentSpeed / walkSpeed * .5f);
     animator.SetFloat ("speedPercent", animationSpeedPercent, speedSmoothTime, Time.deltaTime);

 }

 void Move(Vector2 inputDir, bool running) {
     if (inputDir != Vector2.zero) {
         float targetRotation = Mathf.Atan2 (inputDir.x, inputDir.y) * Mathf.Rad2Deg + cameraT.eulerAngles.y;
         transform.eulerAngles = Vector3.up * Mathf.SmoothDampAngle(transform.eulerAngles.y, targetRotation, ref turnSmoothVelocity, GetModifiedSmoothTime(turnSmoothTime));
     }
         
     float targetSpeed = ((running) ? runSpeed : walkSpeed) * inputDir.magnitude;
     currentSpeed = Mathf.SmoothDamp (currentSpeed, targetSpeed, ref speedSmoothVelocity, GetModifiedSmoothTime(speedSmoothTime));

     velocityY += Time.deltaTime * gravity;
     Vector3 velocity = transform.forward * currentSpeed + Vector3.up * velocityY;

     controller.Move (velocity * Time.deltaTime);
     currentSpeed = new Vector2 (controller.velocity.x, controller.velocity.z).magnitude;

     if (controller.isGrounded) {
         velocityY = 0;
     }

 }

 void Jump() {
     if (controller.isGrounded) {
         float jumpVelocity = Mathf.Sqrt (-2 * gravity * jumpHeight);
         velocityY = jumpVelocity;
     }
 }

 float GetModifiedSmoothTime(float smoothTime) {
     if (controller.isGrounded) {
         return smoothTime;
     }

     if (airControlPercent == 0) {
         return float.MaxValue;
     }
     return smoothTime / airControlPercent;
 }

}

![alt text][1] [1]: /storage/temp/96810-2017-06-29-4.png

Whats the problem ? I can add the this code and it gave the error