Score Update for button click - UI Text Throws error

Questions & Answers
1

I created one UI text under canvas.
Buttons are placed under canvas.
UI text is renamed as score. I dragged and dropped it in button. There are four buttons. Four buttons have these script attached.

public Text score;
public void OnButtonClick(int num) {
     score.text = "Score : 1";
}

NullReferenceException: Object reference not set to an instance of an object
Buttons.OnButtonClick (Int32 num) (at Assets/Scripts/Buttons.cs:21)

The 21 line is : core.text = “Score : 1”;
Please help how to fix it.

2

Not sure what was the problem. I deleted that UI text and removed it from script.
I executed the game.

freshly i created new ui button and updated the script. Now it is working!