code: public function getCacheAdapter($namespace)
      {
          // caching is not enabled for a namespace
          if (!$this->isCacheable($namespace)) {
              return null;
          }
  
          // user wants to implements different adapter for different namespaces
          if (is_array($this->cacheOptions->getAdapter())) {
              // checks if adapter of a namespace exists
              if (!isset($this->cacheOptions->getAdapter()[$namespace])) {
                  return null;
              }
              $adapter =  $this->cacheOptions->getAdapter()[$namespace];
          } else {
              // user want to implements one adapter for all namespaces
              $adapter = $this->cacheOptions->getAdapter();
          }
  
          if (is_object($adapter)) {
              return $adapter;
          }
          if ($this->getServiceLocator()->has($adapter)) {
              return $this->getServiceLocator()->get($adapter);
          }
  
          return new $adapter;
      }
docs: Gets cache adapter of a settings namespace
  
  @param  string                                    $namespace
  @return \Zend\Cache\Storage\StorageInterface|null