public function delete($key)
    {
        $key = (string)$key;
        if ($cache = $this->loadCache()) {
            if (isset($cache[$key])) {
                unset($cache[$key]);
                $this->saveCache($cache);
                return $this;
            }
        }
        throw new RunBBException("Error: delete() - Key '{$key}' not found.");
    }