NullReferenceException: Object reference not set to an instance of an object (Unity UI)

Hallo I wrote this script: public void RandomFunction () {

         randomNumber = UnityEngine.Random.Range (0, listCount);
         Debug.Log(Objecte[randomNumber]);
         ergebnis.text = (Objecte[randomNumber]);
     }
 

but the text is not displayed in my game in the Text field.The Debug.Log is working and i used this ui text on an other place in my Script and there it was working. ergebnis.text = "Object "+listCount.ToString () +" was succesfully added"; Please help.