return Collectors.collectingAndThen(
        Collectors.toMap(keyFunction, valueFunction, mergeFunction, LinkedHashMap::new),
        ImmutableMap::copyOf);
  }

  @SuppressWarnings("unchecked") // An empty map works for all types.
  public static <K, V> ImmutableMap<K, V> of() {
    return (ImmutableMap<K, V>) RegularImmutableMap.EMPTY;
  }

  public static <K, V> ImmutableMap<K, V> of(K k1, V v1) {

      if (USE_LEGACY_SERIALIZATION) {
        Object[] keys = new Object[map.size()];
        Object[] values = new Object[map.size()];
        int i = 0;
        // "extends Object" works around https://github.com/typetools/checker-framework/issues/3013
        for (Entry<? extends Object, ? extends Object> entry : map.entrySet()) {
          keys[i] = entry.getKey();
          values[i] = entry.getValue();

      if (USE_LEGACY_SERIALIZATION) {
        Object[] keys = new Object[map.size()];
        Object[] values = new Object[map.size()];
        int i = 0;
        // "extends Object" works around https://github.com/typetools/checker-framework/issues/3013
        for (Entry<? extends Object, ? extends Object> entry : map.entrySet()) {
          keys[i] = entry.getKey();
          values[i] = entry.getValue();