"The object you want to instantiate is null"

Hello,

I keep getting this error when trying to run a snowboard simulation. I don't understand why I'm getting this and don't know how to resolve it. Here is the code below:

using UnityEngine;
using System.Collections;
using System;

//using System.IO.Ports;


public class Coontroller : MonoBehaviour
{
float tilt;
public AudioSource _boardNoise, _windNoise;

public float turnStrength = .1f;

Vector3 velocity;
Vector3 localVel;
float curDir = 0f;
Vector3 curNormal = Vector3.up;
float distGround, distGroundL, distGroundR;
float boardDeltaY;

Rigidbody rg;
public ParticleSystem ps;
ParticleSystem.EmissionModule pe;
public Transform R, L;
public Trail prefabTrail;
public float trailWidth = 0.3f;

int lastTrailId = -1;
Trail trail;
private void Start()
{
pe = ps.emission;
curDir = transform.rotation.eulerAngles.y;
rg = GetComponent<Rigidbody>();
trail = Instantiate(prefabTrail, Vector3.zero, Quaternion.identity);
}

Vector3 normalGround, posGround;

Vector3 localRot;
void Update()
{
//if (Input.GetKeyDown(KeyCode.P)) Application.CaptureScreenshot(System.DateTime.Now.Date.Minute+".png",4);

tilt = Input.GetAxis("Horizontal");

if (Physics.Raycast(L.position, -curNormal, out hit))
{
posGround = hit.point;
distGroundL = hit.distance;
normalGround = hit.normal;
}
if (Physics.Raycast(R.position, -curNormal, out hit))
{
posGround = (posGround + hit.point) / 2f;
if (hit.point.y > posGround.y)
posGround.y = hit.point.y;
distGroundR = hit.distance;
}
distGround = (distGroundL + distGroundR) / 2f;
SnowTrail();
SnowParticle();

}

public Transform snowParticle;
Vector3 offsetSnowParticle = new Vector3(0, 20, 0);
void SnowParticle()
{
snowParticle.position = transform.position + offsetSnowParticle;
}

void SnowTrail()
{
if (distGround < 0.2f)
{
_boardNoise.volume = magnitude / 50f;
lastTrailId = trail.AddSkidMark(posGround, normalGround, trailWidth, lastTrailId);
pe.rateOverTime = magnitude * 20 - 20 ;
localRot = transform.localRotation.eulerAngles;
localRot.z = (distGroundR - distGroundL) * 100;
transform.localRotation = Quaternion.Lerp(transform.localRotation, Quaternion.Euler(localRot), Time.deltaTime * 10);
}
else
{
_boardNoise.volume = 0;
lastTrailId = -1;
pe.rateOverTime = 0;
}
}

float pitch;
RaycastHit hit;
float magnitude;
Vector3 ang;
void FixedUpdate()
{
boardDeltaY = 0;
boardDeltaY += (float)(tilt * (1 + velocity.magnitude / 10f));
ang = transform.eulerAngles;
ang.y += boardDeltaY;
transform.eulerAngles = ang;
velocity = rg.velocity;
localVel = transform.InverseTransformDirection(velocity);
localVel.x -= localVel.x * turnStrength;

//Simulate friction by increasing the drag depending of the speed
magnitude = velocity.magnitude;
if (magnitude < 3)
rg.drag = 0;
else
rg.drag = magnitude / 200f;

_windNoise.volume = 0.2f + magnitude / 40f;
pitch = 0.8f + magnitude / 40f;
_windNoise.pitch = pitch;

rg.angularVelocity = Vector3.zero;
if (distGround > 0.2f)
{
//Air
}
else
{
//On the ground/snow
rg.velocity = transform.TransformDirection(localVel);
}
}
}

Thanks!

 

Change Trail to GameObject.

public Trail prefabTrail;
public GameObject prefabTrail;