NullRerefanceException. Cant access other scripts variable!!

Hello guys. I've been going crazy, I want to AICharactercontroller standart script to run towards main character when Pick up object is picked up.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.AI;
 
 
 public class PlayerController : MonoBehaviour {
     public float speed;
     public Text countText;
     public Text winText;
     UnityStandardAssets.Characters.ThirdPerson.AICharacterControl PoliceRun;
     GameObject Winston;
     private GameObject police;
     public  int count;
     private Rigidbody rb;
     Transform target1;
     private Vector3 place;
     
 
     // Use this for initialization
     void Start() {
         rb = GetComponent<Rigidbody>();
         count = 0;
         SetCountText();
         winText.text = "";
 
         police = GameObject.FindWithTag("Winston");
         PoliceRun = police.GetComponent<UnityStandardAssets.Characters.ThirdPerson.AICharacterControl>();
         target1 = GameObject.FindWithTag("Winston").GetComponent<Transform>();        
     }
 
     // Update is called once per frame
     void Update() {
 
 
     }
 
     private void FixedUpdate()
     {
 
     }
 
     void OnTriggerEnter(Collider other) {
         if (other.gameObject.CompareTag("Pick Up")) ;
         {
             other.gameObject.SetActive(false);
             count = count + 1;
             SetCountText();
             target1 = PoliceRun.target;
             
         }
 
     }
     void SetCountText() {
 
         countText.text = "Collected=" + count.ToString();
         if (count >= 12 )
         {
             winText.text = "WIN!";
         }
     }
     }
 
 
 

NullReferenceException: Object reference not set to an instance of an object PlayerController.OnTriggerEnter (UnityEngine.Collider other) (at Assets/Scripts/PlayerController.cs:50)

I get this error. What can be done for this purpose?