werid array behavior

Hey guys, Im new to Unity, but not to programming. I was implementing my array while encountering strange behaviour.

 public void addToBoard (Tile c)
 {
         c.setActive (false);
         c.setColor (Color.red);
         matrixBoard [0, 0] =  c;
         if(matrixBoard[0,0] == null){
             print("IM and idiot");
         }
 } 
 
 Guess what it prints... :> yep, idiot thing. But WHY ?  Why my array says it's empty, 

while actually I can access my tile by matrixBoard [0, 0] .doSth().