Swapping out a render texture on a Raw Image via c# script.

Can someone PLEASE show me a basic example of how this is done. I have a raw image attached to a panel of the new GUI system. I have a list of gameobjects that Is created at runtime and I can target by hitting the tab key.

I want to be able to switch Render Textures that is on the GUI image to the camera or texture assigned to that camera as I tab through them but am unable to get it to work. I end up with a runtime error of "NullReferenceException: Object reference not set to an instance of an object" my debug shows me the correct render texture is being selected as I hit tab. My raw image is being selected via the inspector. I have tried so many different ways to make this work I cant even count. So no clue what i am doing wrong. I am able to swap a basic image, the objects name and other references on the Panel. I have only been coding for 3 months so still a bit of a noob...

 <pre>
 
 public RawImage rawImg;
 
     public void GetInfoFromSelectedTarget()
             {
                 if (TargetController.instance.selectedTarget.gameObject == null) 
                     {
                         TargetSelected = false;
                         FillImage.fillAmount = 0f;
                         Name.text = null;
                         Race.text = null;
                         Level.text = null;
                         rawImg = null;
                     } 
                 else 
                     {
     
                         Transform tmp = TargetController.instance.selectedTarget;
                         FillImage.fillAmount = tmp.GetComponentInChildren<EnemyHealth> ().e_percHealth;
     
                         
                         Sprite pic1 = tmp.GetComponentInChildren<EnemyInfo> ().MyPic;
      
                         
     Name.text = tmp.GetComponentInChildren<EnemyInfo> ().Name;
                     Race.text = tmp.GetComponentInChildren<EnemyInfo> ().race;
                     Level.text = "Level: " + tmp.GetComponentInChildren<EnemyInfo> ().level.ToString ();
                     txtForRndTxt = tmp.GetComponentInChildren<EnemyInfo> ().RendTxt;
                     rawImg.texture = txtForRndTxt;
 //                    Debug.Log ("i am trying to show this texture: " + tmp.GetComponentInChildren<EnemyInfo> ().RendTxt.ToString());
                 
                     }
             }