NullReferenceException: Object reference not set to an instance of an object

Hey guys i am newbie i try to mak character controller and i use this video but my code does not working and here is my code warning NullReferenceException: Object reference not set to an instance of an object NewPlayer.FixedUpdate () (at Assets/Codes/NewPlayer.cs:15) and this is my code

 using UnityEngine;
 using UnityEngineInternal;
 using System.Collections;
 public class NewPlayer : MonoBehaviour {
     
     public float maxSpeed = .10f;
     bool _sagaBakma = true;
     Animator animasyon;
     void start()
     {
         animasyon = GetComponent<Animator> ();
     }
     void FixedUpdate(){
         float hareket = Input.GetAxis ("Horizontal");
         animasyon.SetFloat ("Speed", Mathf.Abs (hareket));
         rigidbody2D.velocity = new Vector2 (hareket * maxSpeed, rigidbody2D.velocity.y);
         if (hareket > 0 && !_sagaBakma)
                         Flip ();
                 else if (hareket < 0 && _sagaBakma)
                         Flip ();
         
     }
     void Flip(){
         _sagaBakma = !_sagaBakma;
         Vector3 _deger = transform.localScale;
         _deger.x *= -1;
         transform.localScale = _deger;
         
         
     }
 }

tyvm for helping by the warning at animasyon.SetFloat("Speed",MathfAbs(hareket));