public function setListItemCssClass($class)
    {
        if (!is_string($class)) {
            throw new \InvalidArgumentException(
                'Breadcrumbs::setListItemCssClass() only accepts strings, but '
                . (is_object($class) ? get_class($class) : gettype($class))
                . ' given: ' . print_r($class, true)
            );
        }

        $this->listItemCssClass = $class;

        return $this;
    }