NullReferenceException?

I've got a very simple script from a tutorial, but when I try to run it, it gives the NullReferenceException error in the console everytime I press one of the arrow keys.

Anyone that knows what might be wrong with my code?

Learningscript.cs: using UnityEngine; using System.Collections;

 public class LearningScript : MonoBehaviour 
 {
     GameObject capsuleGO;
     Spinner cubeComp;
     
     void start() 
     {
         capsuleGO = GameObject.Find ("Capsule");
         Debug.Log (capsuleGO);
         cubeComp = GameObject.Find ("Cube").GetComponent<Spinner>();
         Debug.Log(cubeComp);
     }
     
     void Update() 
     {
         if (Input.GetKey (KeyCode.LeftArrow)) 
         {
             capsuleGO.GetComponent<Spinner> ().SpinLeft();
         }
         
         if(Input.GetKey (KeyCode.RightArrow))
         {
             capsuleGO.GetComponent<Spinner>().SpinRight();
         }
         
         if(Input.GetKey (KeyCode.UpArrow))
         {
             cubeComp.SpinLeft();
         }
         
         if(Input.GetKey (KeyCode.DownArrow))
         {
             cubeComp.SpinRight();
         }
     }
 }

spinner.cs:

 using UnityEngine;
 using System.Collections;
 
 public class Spinner : MonoBehaviour {
 
 public void SpinLeft()
     {
         transform.Rotate (0, 0, 60 * Time.deltaTime);
     }
 
     public void SpinRight()
     {
         transform.Rotate(0, 0, -60 * Time.deltaTime);
     }
 }