docs: def CheckHashes(self, hashes, unused_external=True):
      """Checks a list of hashes for presence in the store.
  
      Only unique sha1 hashes are checked, if there is duplication in the hashes
      input it is the caller's responsibility to maintain any necessary mappings.
  
      Args:
        hashes: A list of Hash objects to check.
        unused_external: Ignored.
  
      Yields:
        Tuples of (RDFURN, hash object) that exist in the store.
      """
      hash_map = {}
      for hsh in hashes:
        if hsh.HasField("sha1"):
          hash_urn = self.PATH.Add(str(hsh.sha1))
          logging.debug("Checking URN %s", str(hash_urn))
          hash_map[hash_urn] = hsh
  
      for metadata in aff4.FACTORY.Stat(list(hash_map)):
        yield metadata["urn"], hash_map[metadata["urn"]]