Add and destroy instantiated gameobject in linkedlist C#

I have a linked list of instantiated game objects that are prefabs. When I add them I want to access its script component to set its x and y postion info and I get error #2::NullReferenceException: Object reference not set to an instance of an object

I am wanting to destroy the first object from the linked list and destroy it so it is no longer in the scene. I have tried destroy, but it unity cant destroy a linkedlist game object, only regular objects. I have tried casting it to gameobject, but that doesn't work either. Here is error#1 that I get: error CS0029: Cannot implicitly convert type System.Collections.Generic.LinkedListNode<UnityEngine.GameObject>' to UnityEngine.GameObject'

Any help would be appreciated.

 private static LinkedList<GameObject> PlatUD = new LinkedList<GameObject> ();
 private static LinkedList<GameObject> PlatLR = new LinkedList<GameObject> ();
 private LRPlatform LRscript;
 private UpDownPlatform UDscript;

 if (platNum == 2) { //lR platform
     GameObject Plat = Instantiate (PlatAB, posXY, Quaternion.identity) as   GameObject; // instantiate the platform
     LRscript = Plat.GetComponent<LRPlatform> ();//the platform is a prefab so get the script component of it. I get error #2 here
     LRscript.setPosy (y); //set its y postion
     LRscript.setPosx (x); //set x position
     PlatLR.AddLast (Plat); //add platform to the linked list
    }

 //in update in another if statement I get error #1 when trying to destroy
     if (PlatUD.Count != 0) {
                     GameObject P = PlatUD.First; //get error #1 here
             PlatUD.RemoveFirst ();
             Destroy(P);
   
     }
     if (PlatLR.Count != 0) {
                 GameObject P = PlatLR.First; //and error#1 here
             PlatLR.RemoveFirst ();
             Destroy(P);
     }