NullReferenceException

using UnityEngine;
using System.Collections;
/// <summary>
/// This class handles the movement of a pathed projectile
/// </summary>
public class PathedProjectile : MonoBehaviour
{
    /// The effect to instantiate when the object gets destroyed
    public GameObject DestroyEffect;
    /// the destination of the projectile
    private Transform _destination;
    /// the movement speed
    private float _speed;
 
    /// <summary>
    /// Initializes the specified destination and speed.
    /// </summary>
    /// <param name="destination">Destination.</param>
    /// <param name="speed">Speed.</param>
    public void Initialize(Transform destination, float speed)
    {
        _destination=destination;
        _speed=speed;
    }
 
    /// <summary>
    /// Every frame, me move the projectile's position to its destination
    /// </summary>
    void Update () 
    {
        transform.position=Vector3.MoveTowards(transform.position,_destination.position,Time.deltaTime * _speed);
        var distanceSquared = (_destination.transform.position - transform.position).sqrMagnitude;
        if(distanceSquared > .01f * .01f)
            return;
        
        if (DestroyEffect!=null)
        {
            Instantiate(DestroyEffect,transform.position,transform.rotation); 
        }
        
        Destroy(gameObject);
    }   
}

    void Update () 
{
 if (_destination == null) 
 {
  Debug.Log("_destination is NULL");
  return;
 }