code: protected Set<Radio> getRadioChildren(final Widget widget, final Set<Radio> c) {
          Set<Radio> children = c;
          if (children == null) {
              children = new HashSet<Radio>();
          }
          if (widget instanceof Radio) {
              children.add((Radio) widget);
          } else if (widget instanceof HasOneWidget) {
              children = getRadioChildren(((HasOneWidget) widget).getWidget(), children);
          } else if (widget instanceof HasWidgets) {
              for (Widget w : (HasWidgets) widget) {
                  if (w instanceof Radio) {
                      children.add((Radio) w);
                  } else {
                      children = getRadioChildren(w, children);
                  }
              }
          }
          return children;
      }
docs: Gets the radio children.
  
  @param widget the widget
  @param c the current children
  @return the radio children