code: @CheckForNull
      public T newInstanceFromRadioList(JSONObject parent, String name) throws FormException {
          return newInstanceFromRadioList(parent.getJSONObject(name));
      }
docs: Creates a new instance of a {@link Describable}
  from the structured form submission data posted
  by a radio button group.
  @param parent JSON, which contains the configuration entry for the radio list
  @param name Name of the configuration entry for the radio list
  @return new instance or {@code null} if none was selected in the radio list
  @throws FormException Data submission error