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