static <A, B> Map<A, B> mapPutOrCreate_multi(Map<A, B> map, O... keysAndValues) {
  for (int i = 0; i+1 < l(keysAndValues); i += 2) {
    A key = cast keysAndValues[i];
    B value = cast keysAndValues[i+1];
    map = mapPutOrCreate(map, key, value);
  }
  ret map;
}

Began life as a copy of #1024478