List error c#

I am trying to load images in my resource folder so that I can cycle through them during run time to animate 2D characters. I am getting an error when I try to Add the textures into the array. I'm new to this List...normally I use arrays. Anyone see the mistake?

using UnityEngine; using System.Collections; using System.Collections.Generic;

 public class ImageAnimation : MonoBehaviour 
 {
     
     public string fileName;
     public bool loop;
     
     private float pictureRateInSeconds = 0.04166666666666666666f;
     private List<Texture2D> imagePictures;
      private int imageCounter;
      
     void Start()
     {
         imagePictures = new List<Texture2D>();    
         
     }
     
     
 
     void InitializeImage(string fileName)
     {
         Object[] imageTextures; 
         imageTextures = Resources.LoadAll( "TestImages", typeof(Texture2D));
         for(var i = 0; i < imageTextures.Length; i++)
         {
               imagePictures.Add(imageTextures[i] );
         }
         
         
         
     }