public function getConfigurable($group = null)
    {
        if (empty($this->configurable)) {
            foreach ($this->customfields as $category => $customfield) {
                foreach ($customfield as $field) {
                    if (!$field->configurable()) {
                        continue;
                    }
                    $this->configurable[strtolower(last(explode('\\', $category)))][] = $field->getName();
                }
            }
        }
        return !is_null($group) ? array_get($this->configurable, $group, []) : $this->configurable;
    }