Why is this script for a "Heating Aura" not working? Unity 2D C#

Question

I'm using Microsoft Visual Studio.

I've been trying to make a "heating" script for an empty sprite with a CircleCollider2D, but everything I do doesn't work. I made a Freezing script so that the player would slowly freeze, and I wanted them to be able to replenish their "temp" with a campfire; via an aura around it. Basically a health bar, and a healing aura.

There isn't much about healing auras online, I could find a bit about Coroutines. One video on YouTube had exactly what I was looking for (https://www.youtube.com/watch?v=KE9BHGgVP4A). I found many tutorials on health pickups, but they don't help with what I'm trying to accomplish.

The code didn't work, so I tinkered with it to try and fix it. Now it's throwing the error, "NullReferenceException: Object reference not set to an instance of an object Warmth.OnTriggerEnter2D (UnityEngine.Collider2D col) (at Assets/Scripts/Warmth.cs:19)" Although, I think their may be more errors than this one.

Here is the Code:

using System.Collections;

using UnityEngine;

public class Warmth : MonoBehaviour
{
// Refrence to Freezing component (Basically the players "Health")
private Freezing frz;
public GameObject Player; // Reference to Player component

private void Start()
{
    // Shortens GetComponent to frz (Getting component "Freezing", to get "currentTemp")
    frz = GetComponent<Freezing>();
    Player = GetComponent<GameObject>(); // Shortens GetComponent to Player
}

void OnTriggerEnter2D(Collider2D col) // When Collider enters GameObject
{
    // If GameObject's name is equal to Player, and currentTemp is less then 100
    if (col.gameObject.name.Equals("Player") && frz.currentTemp < 100)
    { StartCoroutine("Warm"); } // Start Coroutine Warm
}

void OnTriggerExit2D(Collider2D col) // When Collider exits GameObject
{
    // If GameObject's name is equal to Player
    if (col.gameObject.name.Equals("Player"))
    { StopCoroutine("Warm"); } // Stop Coroutine Warm
}

IEnumerator Warm()
{
    // Check currentTemp's current amount, while currentTemp is less than or equal to 100, add value 1
    for (float currentTemp = frz.currentTemp; currentTemp <= 100; currentTemp += 1f)
    {
        frz.currentTemp = currentTemp;
        // Time.deltaTime slows each loop
        yield return new WaitForSeconds(Time.deltaTime);
    }
    frz.currentTemp = 100; // Sets Temp to 100 at the end of the loop
}

}

Just in case the problem is in the other script, I will post that too.

Here is the code for the "Freezing" script:

using UnityEngine;

using UnityEngine.UI;

public class Freezing : MonoBehaviour
{

public float startingTemp = 100; //Starting Temp
public float currentTemp;  //Current Temp
public Slider tempSlider; //Refrence for TempatureBar

private bool isFroze; //To check if player froze to death
private Animator anim; //Reference to the Animator component.
private PlayerController pc; //Refrence to the PlayerController component

private void Start()
{
    // Shortens GetComponent to anim.
    anim = GetComponent<Animator>();
    // Shortens GetComponent to pc
    pc = GetComponent<PlayerController>();
}

void Awake()
{
    // Set the initial temp of the player.
    currentTemp = startingTemp;
}

private void Update()
{
    if (isFroze == false) //Makes sure player isn't already dead
    { currentTemp -= Time.deltaTime; } //Minus player temp by deltatime

    // Set the temp bar's value to the current temp.
    tempSlider.value = currentTemp;

    if (currentTemp < 0) //Checks if temp is 0
    {
        //Enables death animation
        isFroze = true;
        //Disables PlayerController
        pc.enabled = false;
    }

    anim.SetBool("isFroze", isFroze); //Set isFroze to isFroze in the animator

}

}

Thanks to anyone who helps! This project I'm working on is a little game I've been building to learn more about C# and Unity, which I've done most of the programming including the Freezing script without many online tutorials, but this one has had me stumped for the past two days; I decided it was time to ask for help.

So, if you'd like to take out the time to explain anything else I've done wrong, I'd be grateful.