code: private function readCachedGroupData(string $namespace) {
  		// Due to confusion, no cached items are returned during development
  		if (N2N::isDevelopmentModeOn()) return null;
  
  		$groupData = null;
  		try {
  			$cacheItem = $this->cacheStore->get(self::APP_CACHE_PREFIX . $namespace, array());
  			if ($cacheItem === null) return null;
  
  			if ($cacheItem->data instanceof GroupData) {
  				return $cacheItem->data;
  			}
  		} catch (CorruptedCacheStoreException $e) {
  		}
  
  		$this->clearCache($namespace);
  		return null;
  	}
docs: Finds cached {@see GroupData} by given namespace.
  If dbtext cache of namespace is corrupt it is cleared.
  
  @param string $namespace
  @return GroupData|mixed|null