Object Reference not set somewhere in the List, but can't figure it out.

public class FruitEditor : MonoBehaviour {

 public GameObject match;
 internal float duration = 1.0f;
 internal int randomInt;

 // Renderers
 internal Renderer _renderer; // Renderer Match Object

 internal Texture2D diffuseMap;
 internal Texture2D specularMap;

 internal float colorValue;
 internal float shininessValue;
 internal float value3;

 // Texture Color, Outline Color & Outline Thickness.
 internal Color _color;
 internal Color _outlineColor;
 internal float _outlineThickness;

 // Textures to assign that have been generated.
 public Texture2D _diffuseTex; // Target Texture
 public Texture2D _gradientTex; // Target Texture

 // Texture Lists's (Diffuse Map, Gradient Ramp)
 internal List<Texture2D> DiffuseMaps = new List<Texture2D>();     // 10 textures
 internal List<Texture2D> GradientMaps = new List<Texture2D>();    // 10 textures

 internal bool mSwitchDiffuse = false;
 internal bool mSwitchGradient = false;


 void Awake()
 {

     foreach (object o in Resources.LoadAll("DiffuseMaps"))
     {
         Texture2D _newTex1 = o as Texture2D;
         DiffuseMaps.Add (o as Texture2D);
     }

     foreach (object p in Resources.LoadAll("GradientRamps"))
     {
         Texture2D _newTex2 = p as Texture2D;
         GradientMaps.Add (p as Texture2D);
     }

 }

 void Start () 
 {

     match = GameObject.FindWithTag("match");
     _renderer = match.GetComponent<Renderer>();
     _renderer.enabled = true;


     _renderer.material.mainTexture = _diffuseTex;
     _renderer.material.SetTexture ("Toon Ramp (RGB)", _gradientTex);

 }

 void Update()
 {

     randomInt = (int)Mathf.Round (Random.Range (0.0f, 9.0f));

     if (!_renderer) {         
         _renderer = match.GetComponent<Renderer> ();
         _renderer.enabled = true;
     }

     if (Input.GetKeyUp(KeyCode.D))
     {
         mSwitchDiffuse = true;
     }

     if (mSwitchDiffuse) 
     {
         Debug.Log ("Switch Diffuse");
         mSwitchDiffuse = false;

         Debug.Log ("DiffuseMap value: "+DiffuseMaps[randomInt]);
         _renderer.material.mainTexture =  DiffuseMaps[randomInt];
     }

     if (Input.GetKeyUp(KeyCode.G))
     {            
         mSwitchGradient  = true;
     }

     if (mSwitchGradient) 
     {
         Debug.Log ("Switch Gradient");
         mSwitchGradient = false;

         _renderer.material.SetTexture ("Toon Ramp (RGB)",GradientMaps[randomInt]);
     }
 }

}