Checkpoints between scenes (NullReferenceException?)

Hi! I am creating my first dungeon crawler game in Unity and am in need of assistance. I want to use a checkpoint system so that after collecting an object in a scene, my game changes the player's starting position upon returning to a different scene. Ex. If the collectible from level 2 is found, when the player returns to level 1 they will start in a different position.

I tried to do t$$anonymous$$s by creating a public variable in a public global control class to hold the position between scenes, w$$anonymous$$ch can hold the position of the local checkpoint and return it when the player comes back to the checkpoint level. T$$anonymous$$s however, causes the following error when called:

NullReferenceException: Object reference not set to an instance of an object.

Below is my Checkpoint class in w$$anonymous$$ch I attempt to

 public static Vector3 checkpointPos;
 public static GameObject player;
 //Lists all gatepoints in the scene
 public static GameObject[] Checkpoints;
 //public instance of a class
 public static Checkpoint instance;

 void Awake()
 {
     //Finds all checkpoints in the current scene
     Checkpoints = GameObject.FindGameObjectsWithTag("Checkpoint");
     //Assigns player object to the player itself
     player = GameObject.FindGameObjectWithTag("Player");
     FindCheckpoint();
 }
 /*Determine w$$anonymous$$ch checkpoint to use based on # of collectibles
 **Ex. If player has not collected 2 collectibles when in gates scene,
 **it will return to the door to Level 2 until otherwise.*/
 public void FindCheckpoint()
 {
     switch (CollectibleControls.collectibles)
     {
         case 1:
             print("Called case 1");
             checkpointPos = Checkpoints[0].transform.position;
             break;
         case 2:
             print("Called case 2");
             checkpointPos = Checkpoints[1].transform.position;
             break;
         case 3:
             print("Called case 3");
             checkpointPos = Checkpoints[2].transform.position;
             break;
         case 4:
             print("Called case 4");
             checkpointPos = Checkpoints[3].transform.position;
             break;
     }
     SavePositions();
 }
 //determine if the global variable is holding a checkpoint; if not,
 //it will find one based on the number of collectibles
 public void DeterminePosition()
 {
     if (GlobalControl.checkpointPos != null)
     {
         player.transform.position = GlobalControl.checkpointPos;
     }
     else
     {
         FindCheckpoint();
     }
 }
 void SavePositions()
 {
     //Save positions to Global control to keep between scenes
     GlobalControl.checkpointPos = checkpointPos;
 }

And here is my variable in global control: public class GlobalControl : MonoBehaviour { public static Vector3 checkpointPos; } It is called only by my game manager when the player returns to the scene with the checkpoint system, w$$anonymous$$ch is referred to as gateLevel:

 public void LevelControls(Collider other)
 {
     SceneManager.LoadScene(doorLevel);
     if (doorLevel == gateLevel)
         Checkpoint.instance.DeterminePosition();
 }

Thank you so much for reading t$$anonymous$$s! I am new to the Unity community and would greatly appreciate the help.