How to get which radio button is not selected in a DHTMLX form

Suite and Optimus Suite 5
#1

I am trying to get the value/name of radio button not selected in a DHTMLX form, I tried different API but was not able to get the result.

#2

There is only the method allowing to get the checked radio button:
https://docs.dhtmlx.com/api__dhtmlxform_getcheckedvalue.html