NavMesh agent bug

I have an enemy and my character. Between them there is a wall. and the enemy should go around the wall to get to the character (using navMesh.setDestination() function), But he doesnt. he tries to go through the wall.

If I use any other empty object as the target of the navMesh the enemy goes around the wall. I tried changing the y position of the gameObject to see if its about the y but it didnt matter. Any help?? Thank you!

Here is the script:

 public float patrolSpeed = 2f;                          // The nav mesh agent's speed when patrolling.
 public float chaseSpeed = 5f;                           // The nav mesh agent's speed when chasing.
 public float chaseWaitTime = 5f;                        // The amount of time to wait when the last sighting is reached.
 public float patrolWaitTime = 1f;                       // The amount of time to wait when the patrol way point is reached.
 public Transform[] patrolWayPoints;                     // An array of transforms for the patrol route.
 
 
 private EnemyAnimation enemySight;                          // Reference to the EnemySight script.
 private NavMeshAgent nav;                               // Reference to the nav mesh agent.
 private Transform player;                               // Reference to the player's transform.
 private float chaseTimer;                               // A timer for the chaseWaitTime.
 private float patrolTimer;                              // A timer for the patrolWaitTime.
 private int wayPointIndex;                              // A counter for the way point array.
 
 
 void Awake ()
 {
     // Setting up the references.
     enemySight = GetComponent<EnemyAnimation>();
     nav = GetComponent<NavMeshAgent>();
     player = GameObject.FindGameObjectWithTag("Player").transform;
 }
 
 
 void Update ()
 {
 
     if(enemySight.InSight)

         Chasing();        

     else
         // ... patrol.
         Patrolling();
 }
 
 

 
 void Chasing ()
 {
     nav.SetDestination( player.transform.position) ;
     
 }
 
 
 void Patrolling ()
 {
     // Set an appropriate speed for the NavMeshAgent.
     nav.speed = patrolSpeed;
     
     // If near the next waypoint or there is no destination...
     if(!enemySight.InSight )
     {
         // ... increment the timer.
         patrolTimer += Time.deltaTime;
         
         // If the timer exceeds the wait time...
         if(patrolTimer >= patrolWaitTime)
         {
             // ... increment the wayPointIndex.
             if(wayPointIndex == patrolWayPoints.Length - 1)
                 wayPointIndex = 0;
             else
                 wayPointIndex++;
             
             // Reset the timer.
             patrolTimer = 0;
         }
     }
     else
         // If not near a destination, reset the timer.
         patrolTimer = 0;
     
     // Set the destination to the patrolWayPoint.
     nav.destination = patrolWayPoints[wayPointIndex].position;
 }