NullReferenceException: Object reference not set to an instance of an object
PietonAnimationEscalier.Update () (at Assets/SCRIPT/PietonAnimationEscalier.cs:12)

using UnityEngine;
using System.Collections;

public class PietonAnimationEscalier : MonoBehaviour {
	
	private TrajetVl trajetVl;
	public Animation anim;
	public string idle, walk, montee, descente;
	public bool chien;
	
	void Update () {
		if (trajetVl.kmh != trajetVl.kmh) {
			UpdateAnimation (trajetVl.kmh);
			trajetVl.kmh = trajetVl.kmh;
		}
	}
	
	private void UpdateAnimation (float _speed) {
		switch ((int)Mathf.Round(_speed*10)) {
		case 0: anim.Play (idle);
			break;
		case 48: anim.Play (descente);
			break;
		case 49: anim.Play (montee);
			break;
		default: anim.Play (walk);
			break;
		}
	}
}