Cannot assign variable agents for clicking a button

I have a script which auto generates some buttons and this works fine. When you click on a button the player is meant to move to the location specified by the button. However when clicking on the button nothing happens. The script that does this is:

using UnityEngine; using System.Collections; using UnityEngine.EventSystems; using UnityEngine.UI;

public class ButtonClick : MonoBehaviour {

 private GameObject marker;
 private UnityEngine.AI.NavMeshAgent agent;
 Vector3 destination;
 
 public GameObject Player;
 //public GameObject Floor1;
 public GameObject Floor2;
 //public GameObject Floor3;
 //public GameObject Floor4;

 public GameObject blob;                
 Vector3 lastpos;
 Vector3 startingposition;
 float Timer = 0.25f;

 void Awake(){
     lastpos = Player.transform.position;
     startingposition = Player.transform.position;
 }

 void Start() {
     agent = gameObject.GetComponent<UnityEngine.AI.NavMeshAgent>();
 }

 void Update() {
     if (Player.transform.position.y < 0.9) {
         Floor2.SetActive(false);

     }
     if (Player.transform.position.y > 0.9) {
         Floor2.SetActive(true);

     }
     Vector3 currpos = Player.transform.position;
     Timer -= Time.deltaTime;
     if (Timer <= 0f) {
         if ((lastpos - currpos).magnitude > 0.001) {
             Spawn ();
         }
         Timer = 0.25f;
     }
     lastpos = currpos;
 }

 void Spawn () {
     Vector3 spawnpos = Player.transform.position;
     Quaternion spawnrot = Player.transform.rotation;
     Instantiate (blob, spawnpos, spawnrot);
 }

 public void markerclick(){
     var markername = EventSystem.current.currentSelectedGameObject.name;
     //Debug.Log (markername);

     var blobs = GameObject.FindGameObjectsWithTag ("blob");
     for (var i=0;i< blobs.Length;i++){
         Destroy(blobs[i]);
     }
     marker = GameObject.Find(markername);
     destination = marker.transform.position;
     //Debug.Log(destination);
     agent.destination = destination;
     //Debug.Log(agent.destination);
 }
     

}

The error i get is:

UnassignedReferenceException: The variable agent of ButtonClick has not been assigned. You probably need to assign the agent variable of the ButtonClick script in the inspector. UnityEngine.AI.NavMeshAgent.set_destination (Vector3 value) (at C:/buildslave/unity/build/artifacts/generated/common/modules/AI/NavMeshAgentBindings.gen.cs:43) ButtonClick.markerclick () (at Assets/ButtonClick.cs:69) UnityEngine.Events.InvokableCall.Invoke (System.Object[] args) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:153) UnityEngine.Events.InvokableCallList.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:634) UnityEngine.Events.UnityEventBase.Invoke (System.Object[] parameters) (at C:/buildslave/unity/build/Runtime/Export/UnityEvent.cs:769) UnityEngine.Events.UnityEvent.Invoke () (at C:/buildslave/unity/build/Runtime/Export/UnityEvent_0.cs:53) 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()

Any ideas?