public synchronized void put(K key, V... values) {
    myKey2Values.merge(key, values, (/*@NotNull*/ arr1, arr2) -> ArrayUtil.mergeArrays(arr1, arr2, arrayFactory()));
    for (V value : values) {
      myValue2Keys.put(value, key);
    }
  }
public synchronized void put(K key, V... values)