Unity 3D, C# и проблема с кодом

Помогите пожалуйста, скачал ассет для Unity3D (2018.4.6f1) и "выскочила" ошибка :
Assets\!Realistic FPS Prefab Files\Scripts\AI\NPCAttack.cs(22,9): error CS0246: The type or namespace name 'ParticleEmitter' could not be found (are you missing a using directive or an assembly reference?)

Вот и код:
using UnityEngine;
using System.Collections;

public class NPCAttack : MonoBehaviour {
private Transform myTransform;
public float range = 100.0f;
public float inaccuracy = 0.5f;
public float fireRate = 0.097f;
public float force = 20.0f;
public float damage = 10.0f;
private float damageAmt;
public int bulletsPerClip = 50;
public int ammo = 150;
public float reloadTime = 1.75f;

private bool canShoot = true;
private bool shooting = false;
private bool reloading = false;
private bool mFlashState = false;
private float recoveryTime = 0.0f;

public ParticleEmitter hitParticles;
public Renderer muzzleFlash;

public AudioClip firesnd;
public AudioClip reloadsnd;
public AudioClip noammosnd;

private int bulletsLeft = 0;

private float shootStartTime = 0.0f;
private float shootElapsedTime = 0.0f;

void Start (){

myTransform = transform;

hitParticles = GetComponentInChildren();

// We don't want to emit particles all the time, only when we hit something.
if (hitParticles){
hitParticles.emit = false;
}

bulletsLeft = bulletsPerClip;
shootStartTime = -fireRate * 2;
}

void Update (){

//run shot timer
shootElapsedTime = Time.time - shootStartTime;

if(shootElapsedTime >= fireRate){
shooting = false;
}

}

void LateUpdate (){

//enable muzzle flash
if (muzzleFlash){
if(shootElapsedTime < fireRate / 3){
if(mFlashState){
muzzleFlash.enabled = true;
mFlashState = false;
}
}else{
if(!mFlashState){
// We didn't, disable the muzzle flash
muzzleFlash.enabled = false;
}
}
}

}

void Fire (){

if (bulletsLeft == 0){
return;
}

//fire weapon
if(!reloading){
if(canShoot){
if(!shooting){
//check sprint recovery timer so gun only shoots after returning to center
if(recoveryTime + 0.5f < Time.time){
FireOneShot();
shootStartTime = Time.time;
shooting = true;
}
}else{
if(shootElapsedTime >= fireRate){
shooting = false;
}
}
}
}else{
shooting = false;
}

}

void FireOneShot (){

//No shooting when sprinting
if (canShoot){
AI AIComponent = myTransform.GetComponent();
Transform target = AIComponent.target;
RaycastHit hit;

Vector3 targetPos = new Vector3(target.position.x + Random.Range(-inaccuracy, inaccuracy),
target.position.y - (AIComponent.eyeHeight / 2) + Random.Range(-inaccuracy, inaccuracy),
target.position.z + Random.Range(-inaccuracy, inaccuracy));
Vector3 targetDir = targetPos - myTransform.position;
Vector3 rayOrigin = new Vector3(myTransform.position.x, myTransform.position.y + AIComponent.eyeHeight, myTransform.position.z);
// Did we hit anything?
if (Physics.Raycast(rayOrigin, targetDir, out hit, range)) {
// Apply a force to the rigidbody we hit
if (hit.rigidbody){
hit.rigidbody.AddForceAtPosition(force * targetDir / (Time.fixedDeltaTime * 100.0f), hit.point);
}
// Place the particle system for spawing out of place where we hit the surface!
// And spawn a couple of particles
if (hitParticles) {
hitParticles.transform.position = hit.point;
hitParticles.transform.rotation = Quaternion.FromToRotation(Vector3.up, hit.normal);