code: def ReadHashBlobReferences(self, hashes, cursor):
      
      query = ("SELECT hash_id, blob_references FROM hash_blob_references WHERE "
               "hash_id IN {}").format(mysql_utils.Placeholders(len(hashes)))
      cursor.execute(query, [hash_id.AsBytes() for hash_id in hashes])
      results = {hash_id: None for hash_id in hashes}
      for hash_id, blob_references in cursor.fetchall():
        sha_hash_id = rdf_objects.SHA256HashID.FromBytes(hash_id)
        refs = rdf_objects.BlobReferences.FromSerializedString(blob_references)
        results[sha_hash_id] = list(refs.items)
      return results
docs: Reads blob references of a given set of hashes.