Help with RubyController on the Ruby's Adventure 2D animating section

So I have no idea whats going wrong can someone have a look at this code for the RubyController and let me know where it is going wrong. The error that is showing up is this:
"NullReferenceException: Object reference not set to an instance of an object RubyController.Update () (at Assets/Scripts/RubyController.cs:43)"
When I start the game the Bots work properly but Ruby is stuck in the left idle animation and won't respond to key presses.
Here's my code:

Code (CSharp):

1. public class RubyController : MonoBehaviour
2. {
3.     public float speed = 3.0f;
4.    
5.     public int maxHealth = 5;
6.     public float timeInvincible = 2.0f;
7.    
8.     public int health {  get { return currentHealth; }}
9.     public int currentHealth;
10.     bool isInvincible;
11.     float invincibleTimer;
12.     Animator animator;
13.     Vector2 lookDirection = new Vector2(0,-1);
14.    
15.     Rigidbody2D rigidbody2d;
16.    
17.     // Start is called before the first frame update
18.     void Start()
19.     {
20.         rigidbody2d = GetComponent<Rigidbody2D>();
21.  
22.         currentHealth = maxHealth;
23.     }
24.  
25.     // Update is called once per frame
26.     void Update()
27.     {
28.         float horizontal = Input.GetAxis("Horizontal");
29.         float vertical = Input.GetAxis("Vertical");
30.                
31.         Vector2 move = new Vector2(horizontal, vertical);
32.        
33.         if(!Mathf.Approximately(move.x, 0.0f) || !Mathf.Approximately(move.y, 0.0f))
34.         {
35.             lookDirection.Set(move.x, move.y);
36.             lookDirection.Normalize();
37.         }
38.        
39.         animator.SetFloat("Look X", lookDirection.x);
40.         animator.SetFloat("Look Y", lookDirection.y);
41.         animator.SetFloat("Speed", move.magnitude);
42.        
43.         Vector2 position = rigidbody2d.position;
44.        
45.         position.x = position.x + speed * horizontal * Time.deltaTime;
46.         position.y = position.y + speed * vertical * Time.deltaTime;
47.         rigidbody2d.MovePosition(position);
48.  
49.         if (isInvincible)
50.         {
51.             invincibleTimer -= Time.deltaTime;
52.             if (invincibleTimer < 0)
53.                 isInvincible = false;
54.         }
55.     }
56.  
57.     public void ChangeHealth(int amount)
58.     {
59.         if (amount < 0)
60.         {
61.             if (isInvincible)
62.                 return;
63.            
64.             isInvincible = true;
65.             invincibleTimer = timeInvincible;
66.         }
67.        
68.         currentHealth = Mathf.Clamp(currentHealth + amount, 0, maxHealth);
69.        
70.         Debug.Log(currentHealth + "/" + maxHealth);
71.     }
72. }

If someone could let me know where it is going wrong that would be fantastic thanks!