Instantiate giving a NullReferenceError

Let me start by saying I'm new to Unity. I have a class that calls the SpawnFloor() function from the Spawner class. Because I'm not sure where the error is, I've posted the whole Spawner class below.

 using UnityEngine;
 using System.Collections;
 
 public class Spawner : MonoBehaviour {
     //Number of unique floors
     static int NumberOfUniqueFloors = 4;
     //List of floors
     public GameObject[] FloorsArray = new GameObject[NumberOfUniqueFloors];
     
     // Use this for initialization
     void Start () {
         //Add floors to list by tag
         for (int i = 0; i < FloorsArray.Length; i++) {
             FloorsArray[i] = GameObject.Find("Floor" + i);
         }
     }
      
     void Update () {
         
     }
 
     public void SpawnFloor()
     {
         //Random number based on number of floors
         int randomIndex = Random.Range(0, NumberOfUniqueFloors - 1);
         
         //Instantiate a random floor
         Transform theNewFloor;
         theNewFloor = Instantiate(FloorsArray[randomIndex], new Vector3(0, 0, 0), Quaternion.identity) as Transform;
         
         //Debug purposes
         Debug.Log("SpawnFloor called");
         
     }
 }

The game runs fine until it goes to call the SpawnFloor() function in which case I get thousands of the following error:

 NullReferenceException
 UnityEngine.Object.Internal_InstantiateSingle (UnityEngine.Object data, Vector3 pos, Quaternion rot) (at C:/BuildAgent/work/7535de4ca26c26ac/Runtime/ExportGenerated/Editor/UnityEngineObject.cs:72)
 UnityEngine.Object.Instantiate (UnityEngine.Object original, Vector3 position, Quaternion rotation) (at C:/BuildAgent/work/7535de4ca26c26ac/Runtime/ExportGenerated/Editor/UnityEngineObject.cs:82)
 Spawner.SpawnFloor () (at Assets/Game 3 - Marble game/Scripts/Spawner.cs:31)
 ScrollUp.Update () (at Assets/Game 3 - Marble game/Scripts/ScrollUp.cs:30)

This is my first time using Instantiate so I believe that's where I'm going wrong. I've tried quite a few suggestions I found on the internet and all produce the same error. Any help is greatly appreciated and may prevent any more internal bleeding from the slamming of my head on the desk. :)