C# Joystick GetComponent();

An error occurs when you start. Error: NullReferenceException: Object reference not set to an instance of an object CubeController.Update () (at Assets/Scripts/CubeController.cs:16); Please tell me where my mistake.

Script C# IController.cs

 public interface IInputController 
 {
     float GetHorizontal(); 
 }
   

Script C# CubeController.cs

 using UnityEngine;
 using System.Collections;
 
 public class CubeController : MonoBehaviour {
 
     public IInputController InputController;
 
 
     // Use this for initialization
     void Start () {
         InputController = PickInputController ();
     }
     
     // Update is called once per frame
     void Update () {
         transform.Rotate (new Vector3(InputController.GetHorizontal(), 0, 0) );
     }
 
     private IInputController PickInputController ()
     {
         #if UNITY_ANDROID
         var temp = GetComponent<UIController>();
         return temp;
         #endif
 
     }
 }
 

Script C# UIController.cs

 using UnityEngine;
 using System.Collections;
 
 public class UIController : MonoBehaviour, IInputController {
 
     public Texture2D TextUpArrow;
     public Texture2D TextDownArrow;
 
     private Rect _upArrow;
     private Rect _downArrow;
 
     private float _vertical;
     private float _width;
 
     void OnGUI()
     {
         if (Screen.width != _width) 
         {
             int prc = (Screen.height / 100) * 25;
             _upArrow = new Rect(25, Screen.height - prc * 2, prc, prc);
             _downArrow = new Rect(25, Screen.height - prc, prc, prc);
             _width = Screen.width;
         }
         GUI.DrawTexture (_upArrow, TextUpArrow);
         GUI.DrawTexture (_downArrow, TextDownArrow);
 
 
     }
 
     public float GetHorizontal()
     {
         bool downArrowTouch = IsTouchContains (_downArrow);
         bool upArrowTouch = IsTouchContains (_upArrow);
         if (downArrowTouch || upArrowTouch) 
         {
             if (downArrowTouch) 
             {
                 if (_vertical < 1) 
                 {
                     _vertical += Time.deltaTime * 3;
                     Debug.Log(_vertical);
                 }
             } 
             else 
             {
                 if (upArrowTouch) 
                 {
                     if (_vertical > -1) 
                     {
                         _vertical -= Time.deltaTime * 3;
                         Debug.Log(_vertical);
                     }
                 }
             }
         } 
         else 
         {
             _vertical = Mathf.Lerp (_vertical, 0, Time.deltaTime * 5);
         }
         Debug.Log (_vertical);
         return _vertical;
 
 
     }    
 
     private bool IsTouchContains(Rect area)
     {
         bool isCont = false;
         foreach (Touch touch in Input.touches)
         {
             Vector3 tPos = touch.position;
             tPos.y = Screen.height - tPos.y;
             if (area.Contains(tPos))
             {
                 isCont = true;
                 Debug.Log(isCont);
             }
         }
         Debug.Log(isCont);
         return isCont;
     }
 }