NullReference on trying to instantiate a prefab which has been set using scriptable object,Particle giving null reference but works in scene view

I have a scriptable object which holds a prefab of a particle effect.

This scriptable object is passed to a MonoBehavior but throws a null reference exception

 public WeaponItem item;
 public Transform camera;
 public Transform gunPos;
 public Transform firePos;

 float elaspedTime = 0f;
 float fireRate = 0f;

 private void Start()
 {
     fireRate = 1f / item.fireRatePerSecond;
 }

 void Update()
 {
     if(Input.GetButton("Fire1"))
     {
         elaspedTime += Time.deltaTime;

         if (elaspedTime >= fireRate)
         {
             Fire();
             elaspedTime = 0f;
         }
     }
 }

 void Fire()
 {
     Instantiate(item.fireParticle, firePos);
     //Destroy(fireParticle, 0.2f);
 }

Here you can see that the particle is in fact set: https://i.gyazo.com/849fbe99c14d51e784e9b0e3a50decc3.png

And I all I get in return is: NullReferenceException: Object reference not set to an instance of an object