static <A, B> AutoCloseable mapPutStrictlyOrFail(Map<A, B> map, A key, B value) {
  if (!(map != null && key != null && value != null)) null;
  B old = map.get(key);
  if (old == null) {
    map.put(key, value);
    ret -> map.remove(old);
  }
  if (eq(old, value)) null;
  fail("Can't overwrite key " + key + " (old value: " + old + ", new value: " + value);
}