Invalid access to property or key 'transform' on a base object of type 'Nil'

Godot Version
version 4.3

Question
I’ve been following the StayAtHomeDev’s tutorial how to make a basic movement and camera rotation and at the camera rotation, when i try to start the game, it shows me a blank screen and shows me this warning
image
does anybody know how to fix it?
this is my code

extends CharacterBody3D


const SPEED = 5.0
const JUMP_VELOCITY = 4.5

@export var TILT_LOWER_LIMIT := deg_to_rad(-90.0)
@export var TILT_UPPER_LIMIT := deg_to_rad(90.0)
@export var CAMERA_CONTROLLER : Camera3D

var _mouse_input : bool = false
var _rotation_input : float
var _tilt_input : float
var _mouse_rotation : Vector3
var _player_rotation : Vector3
var _camera_rotation : Vector3

func _unhandled_input(event):
	_mouse_input = event is InputEventMouseMotion and Input.get_mouse_mode() == Input.MOUSE_MODE_CAPTURED
	if _mouse_input:
		_rotation_input = -event.relative.x
		_tilt_input = -event.relative.y
		print(Vector2(_rotation_input,_tilt_input))

func _update_camera(delta):
	
	#Rotate camera using euler rotation
	_mouse_rotation.x += _tilt_input * delta
	_mouse_rotation.x = clamp(_mouse_rotation.x, TILT_LOWER_LIMIT, TILT_UPPER_LIMIT)
	_mouse_rotation.y += _rotation_input * delta
	
	CAMERA_CONTROLLER.transform.basis = Basis.from_euler(_mouse_rotation)
	CAMERA_CONTROLLER.rotation.z = 0.0
	
	_rotation_input = 0.0
	_tilt_input = 0.0

func _ready():
	Input.mouse_mode = Input.MOUSE_MODE_CAPTURED

func _input(event):
		if event.is_action_pressed("exit"):
			get_tree().quit()

func _physics_process(delta):
	# Add the gravity.
	if not is_on_floor():
		velocity += get_gravity() * delta
	
	_update_camera(delta)
	

	# Handle jump.
	if Input.is_action_just_pressed("jump") and is_on_floor():
		velocity.y = JUMP_VELOCITY

	# Get the input direction and handle the movement/deceleration.
	# As good practice, you should replace UI actions with custom gameplay actions.
	var input_dir := Input.get_vector("move_left", "move_right", "move_forward", "move_backward")
	var direction := (transform.basis * Vector3(input_dir.x, 0, input_dir.y)).normalized()
	if direction:
		velocity.x = direction.x * SPEED
		velocity.z = direction.z * SPEED
	else:
		velocity.x = move_toward(velocity.x, 0, SPEED)
		velocity.z = move_toward(velocity.z, 0, SPEED)

	move_and_slide()

Are you assigning the CAMERA_CONTROLLER value on your Inspector?
try to print this variable in the _ready() function to see if it’s being initialized

print(CAMERA_CONTROLLER)

Also, check if the scene that you are trying to run, contain the node being assigned to this variable.