I don't understand NullReferenceException: Object reference not set to an instance of an object

So I'm trying to make a switch to open a door in my fps and I'm getting a null reference when calling on another script "PlayerCasting" Here's my first script the one giving off the error:

 import UnityEngine.UI;
 
 var TextDisplay : GameObject;
 var TheDistance : float = PlayerCasting.DistanceFromTarget;
 
  function Update () {
     TheDistance = PlayerCasting.DistanceFromTarget;
 }
 
     function OnMouseOver () {
     if (TheDistance <= 2) {
         TextDisplay.GetComponent.<Text>().text = "Press Button";
     }
 }
 
 function OnMouseExit () {
     TextDisplay.GetComponent.<Text>().text = "";
 }

The error is occurring at js.4 or the line that starts with var TheDistance In the line, I am calling on TheDistance which is in the other script "PlayerCasting".

Here is the other script that I'm trying to reference:

 static var DistaceFromTarget : float;
 
 var ToTarget : float;
 
 function Update () {
     var hit : RaycastHit;
         if (Physics.Raycast (transform.position, transform.TransformDirection(Vector3.forward), hit)) {
             ToTarget = hit.distance;
             DistanceFromTarget = ToTarget;
         }
 }

What did it do wrong? Any help is appreciated!

Thanks!

-Brendan