Object reference not set to an instance of an object (Unity 2D animation)

Hey guys, I'm currently trying to figure out how to Animate in Unity 2D and with that I stumbled into transitioning. Although I have no idea how to call the transition parameters into code, this is my current attempt which is giving the error above. I dont know why Its giving me the error as in Start() I called the animator component into the script. (full error: NullReferenceException: Object reference not set to an instance of an object MovementFixed.Update () (at Assets/Script/MovementFixed.cs:21) ) Any help would be great! Thanks!

 Animator animator;
 public float speed = 1.5f;
 public int Direction = 0;


     void start(){
     animator = this.GetComponent<Animator>();
 }



 void Update ()
 {
     if (Input.GetKey (KeyCode.LeftArrow)) {
         transform.position += Vector3.left * speed * Time.deltaTime;
         animator.SetInteger("Direction", 1);
     }
     if (Input.GetKey (KeyCode.RightArrow)) {
         transform.position += Vector3.right * speed * Time.deltaTime;
         animator.SetInteger("Direction", 1);
     }
     if (Input.GetKey (KeyCode.UpArrow)) {
         transform.position += Vector3.up * speed * Time.deltaTime;
         animator.SetInteger("Direction", 1);
     }
     if (Input.GetKey (KeyCode.DownArrow)) {
         transform.position += Vector3.down * speed * Time.deltaTime;
         animator.SetInteger("Direction", 1);
     }

 }

}