BinaryOperator<V> mergeFunction) {
    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    checkNotNull(mergeFunction);
    return collectingAndThen(
        Collectors.toMap(keyFunction, valueFunction, mergeFunction, LinkedHashMap::new),
        ImmutableMap::copyOf);
  }

  static <T extends @Nullable Object, K, V>
      Collector<T, ?, ImmutableSortedMap<K, V>> toImmutableSortedMap(

      BinaryOperator<V> mergeFunction) {
    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    checkNotNull(mergeFunction);
    return collectingAndThen(
        Collectors.toMap(keyFunction, valueFunction, mergeFunction, LinkedHashMap::new),
        ImmutableMap::copyOf);
  }

  static <T extends @Nullable Object, K, V>
      Collector<T, ?, ImmutableSortedMap<K, V>> toImmutableSortedMap(