public function erase($key) {
    $cacheData = $this->_loadCache();
    if (true === is_array($cacheData)) {
      if (true === isset($cacheData[$key])) {
        unset($cacheData[$key]);
        $cacheData = json_encode($cacheData);
        file_put_contents($this->getCacheDir(), $cacheData);
      } else {
        throw new Exception("Error: erase() - Key '{$key}' not found.");
      }
    }
    return $this;
  }