Why does collider return null?

Godot Version

4.2.2

Question

I’m currently doing the first 3D game lesson from the docs to get more familiar with Godot and while everything is working I’m confused on how the get_collider method on line 34 can return null. I checked on the documentation for KinematicCollision3D, but it didn’t really explain anything. It’s important to me to know this, because I don’t like copying code without understanding it.

extends CharacterBody3D

# How fast the player moves in meters per second.
@export var speed = 14
# The downward acceleration when in the air, in meters per second squared.
@export var fall_acceleration = 75
@export var jump_impulse = 20
# Vertical impulse applied to the character upon bouncing over a mob in
# meters per second.
@export var bounce_impulse = 16

var target_velocity = Vector3.ZERO


func _physics_process(delta):
	var direction = Vector3.ZERO

	if Input.is_action_pressed("move_right"):
		direction.x += 1
	if Input.is_action_pressed("move_left"):
		direction.x -= 1
	if Input.is_action_pressed("move_back"):
		direction.z += 1
	if Input.is_action_pressed("move_forward"):
		direction.z -= 1
	if is_on_floor() and Input.is_action_just_pressed("jump"):
		target_velocity.y = jump_impulse
# Iterate through all collisions that occurred this frame
	for index in range(get_slide_collision_count()):
		# We get one of the collisions with the player
		var collision = get_slide_collision(index)

		# If the collision is with ground
		if collision.get_collider() == null:
			print("NULL")
			continue
		# If the collider is with a mob
		if collision.get_collider().is_in_group("mob"):
			var mob = collision.get_collider()
			# we check that we are hitting it from above.
			if Vector3.UP.dot(collision.get_normal()) > 0.1:
				# If so, we squash it and bounce.
				mob.squash()
				target_velocity.y = bounce_impulse
				# Prevent further duplicate calls.
				break
	if direction != Vector3.ZERO:
		direction = direction.normalized()
		$Pivot.basis = Basis.looking_at(direction)

	# Ground Velocity
	target_velocity.x = direction.x * speed
	target_velocity.z = direction.z * speed

	# Vertical Velocity
	if not is_on_floor(): # If in the air, fall towards the floor. Literally gravity
		target_velocity.y = target_velocity.y - (fall_acceleration * delta)

	# Moving the Character
	velocity = target_velocity
	move_and_slide()

Hi,
you should call move_and_slide before check the collisions, I think.

Huh, I’m not getting anymore null results. So by calling move_and_slide before checking collisions make sure I get no null results?