Null reference..

I know this quastion is being answered lot of times before, I searched and read lot topics, but none done work for me...

Here is the problem...

I have one class in a separete file that doesen't inheritate from Mono, just store all I need to use in Mono..

Now I have my mono class that is attached to Empty Game object.

This is the simple test, I need to work only OnGUI, everything is going to be 2D.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class test : MonoBehaviour  {

      proba t = new proba(10,10,100,100); //proba constructor and used for myRect

     // Use this for initialization
     void Start () {
     }
     
     // Update is called once per frame
     void Update () {
         if(t.myRect.Contains(Event.current.mousePosition)){
             if(Event.current.type == EventType.MouseUp){
                 t.myRect.x = 0;
             }
         }
     }
     
     void OnGUI(){
         GUI.Box(t.myRect,"");    
     }
 }

I have that little box on screen with parameters i passed to proba... but the problem is I am getting null reference when I want to click on that box, it doesn't know what is t.myRect.x... Everything in proba class is public, and here it is...

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class proba{
 
     public float x;
     public float y;
     public float w;
     public float h;
     public Rect myRect;
     public proba(float X,float Y,float W, float H){
         x = X;
         y = Y;
         w = W;
         h = H;
         myRect = new Rect(x,y,w,h);
     }
 }

NullReferenceException: Object reference not set to an instance of an object

And it is pointing to line 13 in test witch is begining of if statement where I have same check for Event...