Hi, so I am trying to make this little platformer game. I have been working on the Health Bar for a while now because I need to autoload my player script so I can use the "hp" variable in my Health Bar script but everytime I add the player script to Auto Load and start the game the game can not load and I get this error: Attempt to call function 'play' in base 'null instance' on a null instance.

Here is my player script:

extends KinematicBody2D

const SPEED = 350
const GRAVITY = 12
const JUMP_POWER  = -450
const FLOOR = Vector2(0, -1)
const MAXSPEED = 50
const OSTEP = preload("res://Scenes/Spear.tscn")

var velocity = Vector2()
var is_dead = false
var is_on_floor = is_on_floor()
var Enemy = preload("res://Scenes/Enemy.tscn")
var on_ground = false
var is_attacking = false
var hp = 3

func _physics_process(delta: float) -> void:
	if is_dead == false:	
	
		if Input.is_action_pressed("lavo"):    #pohyb dolava
			if is_attacking == false:
				velocity.x = -SPEED
				$AnimatedSprite.play("Run")
				$AnimatedSprite.flip_h = true
				if sign($Position2D.position.x) == 1:
					$Position2D.position.x *= -1
		elif Input.is_action_pressed("pravo"):   #pohyb doprava    
			if is_attacking == false:
				velocity.x = SPEED
				$AnimatedSprite.play("Run")
				$AnimatedSprite.flip_h = false
				if sign($Position2D.position.x) == -1:
					$Position2D.position.x *= -1
		else:    #nehybnost
			velocity.x = 0
			if on_ground == true && is_attacking == false:
				$AnimatedSprite.play("Idle")
			
		if Input.is_action_just_pressed("skok"):    #skok
			if is_attacking == false:
				if on_ground == true:
					$JumpSound.play()
					velocity.y = JUMP_POWER
					on_ground = false
				
		if Input.is_action_just_pressed("hod_ostep") && is_attacking == false:    #hodenie ostepu
			is_attacking = true
			$SpearThrow.play()
			$AnimatedSprite.play("Attack")
			var ostep = OSTEP.instance()
			if sign($Position2D.position.x) == 1:
				ostep.set_ostep_direction(1)
			else:
				ostep.set_ostep_direction(-1)
			get_parent().add_child(ostep)
			ostep.position = $Position2D.global_position
					
					
		for i in range (get_slide_count()):
			var collision = get_slide_collision(i)
			if collision.collider.is_in_group("Enemy"):
				var enemy = collision.collider
				if Vector2.UP.dot(collision.normal) > 0.1:
					enemy.squash()
					velocity.y = JUMP_POWER
		
		velocity.y += GRAVITY
		
		if is_on_floor():    #skok
			on_ground = true
		else:
			if is_attacking == false:
				on_ground = false
				$AnimatedSprite.play("Jump")
				if velocity.y <= 0:
					$AnimatedSprite.play("Jump")
	
	
	velocity = move_and_slide(velocity, FLOOR, true)
	
	
func _on_EnemyDetector_body_entered(body):    #zabitie hraca nepriatelom
	if "Enemy" in body.name and is_dead == false:
		$Hurt.play()
		hp -= 1
		
		if hp == 0:
			_dead()
	elif "Enemy" in body.name and is_dead == true:
		$Timer.start()
		

	
func _dead():
			is_dead == true    #proces smrti
			set_physics_process(false)
			$AnimatedSprite.play("MOREDEAD")
			get_node("CollisionShape2D").disabled = true
			$EnemyDetector/CollisionShape2D.call_deferred("set_disabled", true)
			$DeathSound.play()
			$Timer.start()
			

func _on_Timer_timeout() -> void:    #prepnutie do menu po smrti
	get_tree().change_scene("res://Scenes/TitleScreen.tscn")

func _on_AnimatedSprite_animation_finished() -> void:

Can someone help please, I have been stuck on this for a while now.
Thanks.