Cannot get a variable on a other script

Hey all,

I am 14 years old. Sorry for my English because I speak French. I start with Unity 3D. I make a idle game. I searched on forum but nothing worked.

My code:

Click.cs

 using UnityEngine;
 using System.Collections;
 
 public class Click : MonoBehaviour {
 
     public UnityEngine.UI.Text goldDisplay;
     public  int gold = 0;
     public  int goldperclick = 1;
 
     void Update(){
         goldDisplay.text = "" + gold;
     }
 
     public void Clicked() {
         gold += goldperclick;
     }
 
 }

Upgrade.cs

 using UnityEngine;
 using System.Collections;
 
 public class Upgrade : MonoBehaviour {
 
     private Click clicks;
     
     void Awake(){
         clicks = GetComponent<Click>();
     }
 
     public void UpgradeGPC() {
         if (clicks.gold >= 25) {
             clicks.gold -= 25;
             clicks.goldperclick += 1;
         }
     }
 
 
 }
 

When I click on upgrade button, a error appears.

NullReferenceException: Object reference not set to an instance of an object Upgrade.UpgradeGPC () (at Assets/Scripts/Upgrade.cs:19) UnityEngine.Events.InvokableCall.Invoke (System.Object[] args) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:149) UnityEngine.Events.InvokableCallList.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:626) UnityEngine.Events.UnityEventBase.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:766) UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:54) UnityEngine.UI.Button.Press () (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:35) UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:44) UnityEngine.EventSystems.ExecuteEvents.Execute (IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:52) UnityEngine.EventSystems.ExecuteEvents.Execute[IPointerClickHandler] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.EventFunction`1 functor) (at C:/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/EventSystem/ExecuteEvents.cs:269) UnityEngine.EventSystems.EventSystem:Update()

Thank you for your reply.