code: def _bulk_cache_lookup(self, api_name, keys):
          
          if self._cache:
              responses = self._cache.bulk_lookup(api_name, keys)
              missing_keys = [key for key in keys if key not in responses.keys()]
              return (responses, missing_keys)
  
          return ({}, keys)
docs: Performes a bulk cache lookup and returns a tuple with the results
          found and the keys missing in the cache. If cached is not configured
          it will return an empty dictionary of found results and the initial
          list of keys.
  
          Args:
              api_name: a string name of the API.
              keys: an enumerable of string keys.
          Returns:
              A tuple: (responses found, missing keys).