code: private HelpBlock findHelpBlock(Widget widget) {
          if (widget instanceof HelpBlock) { return (HelpBlock) widget; }
          // Try and find the HelpBlock in the children of the given widget.
          if (widget instanceof HasWidgets) {
              for (Widget w : (HasWidgets) widget) {
                  if (w instanceof HelpBlock) { return (HelpBlock) w; }
              }
          }
          if (!(widget instanceof HasValidationState)) {
              // Try and find the HelpBlock in the parent of widget.
              return findHelpBlock(widget.getParent());
          }
          return null;
      }
docs: Find the sibling {@link HelpBlock}.
  
  @param widget the {@link Widget} to search.
  @return the found {@link HelpBlock} of null if not found.