How to uncheck/check a RadioButton

Hi All.

I have ListView where row has RadioButton and I would like to give a user ability to uncheck a radiobutton through a click on it, while it's checked. When the user decides that he does not want either option and should be allowed to click on RadioButton again to null his decision. All RadioButton in row have different GroupName and have the same GroupName in the columns.

How to make radio button that I want to represent both true and false value?

Thanks.