Array error code

using UnityEngine;
using System.Collections;

public class WallBounce : MonoBehaviour {

    // The player transform
    [SerializeField]
    private Transform playerTransform;

    // Is the player touching a wall?
    public bool wall = false;

    // The layer that the wall is on. Used for collision
    public LayerMask wallLayer;

    // The raduis required to detect a wall collision
    public float range = 10.0f;

    // The amount of degrees to rotate when colliding with a wall
    public float collsionRotation = 180.0f;

    void Awake() {
        playerTransform = gameObject.transform;
    }

    void FixedUpdate()
    {
        // If the car is close to a wall...
        if (Physics.OverlapSphere(transform.position, range, wallLayer)[0] != null)
        {
            // ...set wall to true
            wall = true;
        }
        // If not...
        else {
            // ...set wall to false
            wall = false;
        }

        // Rotate the car 45 degrees if it is touching a wall
        if (wall) {
            playerTransform.Rotate(collsionRotation, 0, collsionRotation, Space.Self);

        }
    }

}