static <A, B> AutoCloseable tempPut(Map<A, B> map, A key, B value) {
  if (map != null) {
    bool wasContained = map.containsKey(key);
    B old = map.put(key, value);
    ret -> { if (wasContained) map.put(key, old); else map.remove(key); };
  }
  null;
}