private function _get_cache_mode($cache_mode)
{
if (empty($cache_mode) || self::CACHE_USE_DEFAULT === $cache_mode) {
$cache_mode = $this->cache_mode;
}
// Fallback if self::$cache_mode did not get a valid value
if (!in_array($cache_mode, self::$cache_modes)) {
$cache_mode = self::CACHE_OBJECT;
}
return $cache_mode;
}