code: public void storeOmemoPreKeys(OmemoDevice userDevice, TreeMap<Integer, T_PreKey> preKeyHashMap) {
          for (Map.Entry<Integer, T_PreKey> entry : preKeyHashMap.entrySet()) {
              storeOmemoPreKey(userDevice, entry.getKey(), entry.getValue());
          }
      }
docs: Store a whole bunch of preKeys.
  
  @param userDevice our OmemoDevice.
  @param preKeyHashMap HashMap of preKeys