Null Reference Exception

I'm working on a game and I've run into a problem that no matter what I try, won't be fixed. Whenever I start the game it gives me this error: NullReferenceException: Object reference not set to an instance of an object GameMaster.Awake () (at Assets/GameMaster.cs:12). And whenever I'm supposed to die it gives me this error: NullReferenceException: Object reference not set to an instance of an object GameMaster.KillPlayer (.Player player) (at Assets/GameMaster.cs:27) Player.DamagePlayer (Int32 damage) (at Assets/Players/Meelee/Scripts/Player.cs:27). Here are the two scripts I'm using: using System.Collections; using UnityEngine;

public class GameMaster : MonoBehaviour {

 public static GameMaster gm;

 void Awake ()
 {
     if(gm == null)
     {
        gm = GameObject.FindGameObjectWithTag("GM").GetComponent<GameMaster>();
     }
 }

 public Transform playerPrefab;
 public Transform spawnPoint;

 public void RespawnPlayer()
 {
     Instantiate(playerPrefab, spawnPoint.position, spawnPoint.rotation);
 }

 public static void KillPlayer(Player player)
 {
     Destroy(player.gameObject);
     gm.RespawnPlayer();
 }

} and using System.Collections; using System.Collections.Generic; using UnityEngine;

public class Player : MonoBehaviour {

 [System.Serializable]
 public class PlayerStats
 {
     public int health = 100;
 }
 public PlayerStats playerStats = new PlayerStats();

 public int fallBoundary;

 void Update()
 {
     if (transform.position.y <= -20)
         DamagePlayer(77777777);             //Just to make sure it's dead... very dead.
 }

 public void DamagePlayer(int damage)
 {
     playerStats.health -= damage;
     if(playerStats.health <= 0)
     {
         GameMaster.KillPlayer(this);
     }
 }
 

}

Thx.