So I know this has been asked before but, I feel this only applies to my problem.

I get the "NullReferenceException: Object reference not set to an instance of an object" error. I usually know what to do but, at this point I cannot figure it out. I'm making a rts game and this code worked before but now gives me trouble. This is the Unit Script:

using UnityEngine;

using System.Collections;

public class Unit : MonoBehaviour {

 public bool selected = false;
 public CameraControl camControl;
 public float speed = 10;
 private Vector3 moveToDest = Vector3.zero;
 public float floorOffset = 1;
 public float stopDistanceOffset;
 public Vector3 destination;
 void Update () {
     //UpdateMove();
     if (GetComponent<Renderer>().isVisible && Input.GetMouseButtonUp(0))
     {
         Vector3 camPos = Camera.main.ScreenToViewportPoint(transform.position);
         camPos.y = camControl.InvertMouseY(camPos.y);
         selected = camControl.selection.Contains(camPos);
         if (selected)
         {
             GetComponent<Renderer>().material.color = Color.red;

         }
         else
         {
             GetComponent<Renderer>().material.color = Color.white;
         }
     }
     if(selected && Input.GetMouseButtonUp(1))
     {
         destination = camControl.GetDestination();
         if (destination != null)
         {
             Debug.Log("Can Move");
             moveToDest = destination;
             NavMeshAgent agent = GetComponent<NavMeshAgent>();
             agent.SetDestination(destination);
             Vector3 direction = (moveToDest - transform.position).normalized;
             transform.GetComponent<Rigidbody>().velocity = direction * speed;
             
             
         }
         else if(transform.position == destination) 
         {
             transform.GetComponent<Rigidbody>().velocity = Vector3.zero;
             
         }
     }
     
 }
 

}

Then here's the Camera Control Script:

using UnityEngine;

using System.Collections;

using System.Collections.Generic;

public class CameraControl : MonoBehaviour {

 public Texture2D selectionHighlight = null;

 public Rect selection = new Rect(0, 0, 0, 0);

 private Vector3 startClick = -Vector3.one;

 public float speed;

 private static Vector3 moveToDestination = Vector3.zero;

 private static List<string> passables = new List<string>() { "Floor" };

 public RaycastHit hitTarget;

 public GameObject target;

 public GameObject targetInstance;
 
 public float ZoomAmount = 0; //With Positive and negative values

 public float MaxToClamp = 10;

 public float ROTSpeed = 10;
 
 void Update () {
     

     ZoomAmount += Input.GetAxis("Mouse ScrollWheel");

     ZoomAmount = Mathf.Clamp(ZoomAmount, -MaxToClamp, MaxToClamp);

     var translate = Mathf.Min(Mathf.Abs(Input.GetAxis("Mouse ScrollWheel")), MaxToClamp -Mathf.Abs(ZoomAmount));

     gameObject.transform.Translate(0, 0, translate * ROTSpeed * Mathf.Sign(Input.GetAxis("Mouse ScrollWheel")));
   
     GameObject unit = GameObject.FindGameObjectWithTag("SelectableUnit");

     if (Input.GetMouseButtonUp(1) && unit.GetComponent<Unit>().selected)
     {
         Destroy(targetInstance);

         targetInstance = Instantiate(target, unit.GetComponent<Unit>().destination, Quaternion.identity) as GameObject;
         
     }
     else if(Input.GetMouseButtonDown(0))
     {
         
         Destroy(targetInstance);
     }
     Cleanup();
     CheckCamera();
     if (Input.GetKey(KeyCode.W))
     {
         transform.Translate(Vector3.up * speed);
     }
     if (Input.GetKey(KeyCode.S))
     {
         transform.Translate(Vector3.down * speed);
     }
     if (Input.GetKey(KeyCode.A))
     {
         transform.Translate(Vector3.left * speed);
     }
     if (Input.GetKey(KeyCode.D))
     {
         transform.Translate(Vector3.right * speed);
     }

 }
 private void OnGUI()
 {
     if(startClick != -Vector3.one)
     {
         GUI.color = new Color(1, 1, 1, 0.5f);
         GUI.DrawTexture(selection, selectionHighlight);
     }
 }
 void CheckCamera()
     {
     if (Input.GetMouseButtonDown(0))
     {
         startClick = Input.mousePosition;

     }
     else if (Input.GetMouseButtonUp(0))
     {
         
         startClick = -Vector3.one;
     }
     if (Input.GetMouseButton(0))
     {

         selection = new Rect(startClick.x, InvertMouseY(startClick.y), Input.mousePosition.x - startClick.x, InvertMouseY(Input.mousePosition.y) - InvertMouseY(startClick.y));

         if (selection.width < 0)
         {
             selection.x += selection.width;
             selection.width = -selection.width;
         }
         if (selection.height < 0)
         {
             selection.y += selection.height;
             selection.height = -selection.height;
         }
     }
  }
 public float InvertMouseY(float y)
 {
     return Screen.height - y;
 }
 private void Cleanup()
 {
     if (!Input.GetMouseButtonUp(1))
     {
         moveToDestination = Vector3.zero;
         
         
     }
 }
 public Vector3 GetDestination()
 {
     if(moveToDestination == Vector3.zero)
     {
         RaycastHit hit;
         Ray r = Camera.main.ScreenPointToRay(Input.mousePosition);
         if(Physics.Raycast(r, out hit))
         {
             
             while (!passables.Contains(hit.transform.gameObject.name))
             {
                 if (!Physics.Raycast(hit.point + r.direction * 0.1f, r.direction, out hit))
                 {
                     
                     break;
                     
                 }
                     
             }
             Debug.Log("Assigned Move Destination");
             moveToDestination = hit.point;
             hitTarget = hit;
         }
             
     }
     
     return moveToDestination;
 }

}

Most of the selection code is from a tutorial on Youtube. Unfortunately I don't know where I went wrong so I don't know where to revert back to.