code: protected function renderItem($link, $template)
      {
          if (isset($link['label'])) {
              $label = $this->encodeLabels ? Html::encode($link['label']) : $link['label'];
          } else {
              throw new InvalidConfigException('The "label" element is required for each link.');
          }
          if($link['options']['class']){
              $label = Html::tag('i', '',$link['options']).$label;
          }
          if (isset($link['url'])) {
              return strtr($template, ['{link}' => Html::a($label, $link['url'])]);
          } else {
              return strtr($template, ['{link}' => $label]);
          }
      }
docs: Renders a single breadcrumb item.
  @param array $link the link to be rendered. It must contain the "label" element. The "url" element is optional.
  @param string $template the template to be used to rendered the link. The token "{link}" will be replaced by the link.
  @return string the rendering result
  @throws InvalidConfigException if `$link` does not have "label" element.