UnassignedReferenceException: The variable closest of TAKE has not been assigned.

the codse that doesn't work, are after the line else of the function OnTriggerStay, witch are:

closest.transform.parent = null;

closest.GetComponent.().useGravity = true;

if I delete those two lines, it work, but otherwise I can't find a reason for that being bad, because just before, I test with this code several times and it worked perfectly, but suddenly this problem showed and I just don't know what happened T^T

PS: I saw that others who has the same problem said that ie because they attach the script with another gameobject? but things are not like that in my case T.T

PS:if i ignore these problems and hit pause again, it work like it should~~ however the problems come back every time i hit play~~~ but if i delete those two lines, the problem is gone with the codes function >.<

please help~~~~ (>^<)

 var Walls : GameObject[];
 var Hand : GameObject;
 var closest : GameObject;
 //var WDirection ;
 //var ADirection ;
 var distance ;
 var Rtime;
 
 function Start () {
 
 Hand = GameObject.FindWithTag("Player");
 
 }
 
 function Update () {
 //WDirection = transform.localPosition.y;
 //ADirection = transform.localPosition.y;
 Rtime = GetComponent.<Animation>()["TAKE"].time;
 
 
 Walls = GameObject.FindGameObjectsWithTag("Respawn");
 for (var Wall:GameObject in Walls){
     distance = Vector3.Distance(Wall.transform.position, Hand.transform.position);
     if (distance<1)
     {
      closest=Wall;
     
             }
         }
     return closest;
     
 }
 
 function OnTriggerEnter(other: Collider) {
     if ((other.gameObject.tag == "Respawn")&&(Input.GetKey(KeyCode.K)))
     {
     print("Enter");
     }
     
 }
 
 
     
 function OnTriggerStay(other: Collider) {
     if ((other.gameObject.tag == "Respawn")&&(Input.GetKey(KeyCode.K))&&(Rtime>0.2 && Rtime<1.1))
     {
     print("Grab");
     
     closest.transform.parent = Hand.transform;
     closest.GetComponent.<Rigidbody>().useGravity = false;
     
     //closest.GetComponent.<Rigidbody>().isKinematic = true;    
     }else{
     closest.transform.parent = null;
     //closest.GetComponent.<Rigidbody>().isKinematic = false;
     closest.GetComponent.<Rigidbody>().useGravity = true;
     
     
   }
 }
     
 function OnTriggerExit(other: Collider) {
     if ((other.gameObject.tag == "Respawn"))
     {
     print("Exit");
     //closest.GetComponent.<Rigidbody>().isKinematic = false;    
     closest.transform.parent = null;
     closest.GetComponent.<Rigidbody>().useGravity = true;
     }
 }