// unboxed
  @J2ktIncompatible
  public void testToTableNullMerge() {
    // TODO github.com/google/guava/issues/6824 - the null merge feature is not compatible with the
    // current nullness annotation of the mergeFunction parameter. Work around with casts.
    BinaryOperator<@Nullable Integer> mergeFunction = (v1, v2) -> null;

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

          Function<? super T, ? extends V> valueFunction,
          BinaryOperator<V> mergeFunction) {
    checkNotNull(comparator);
    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    checkNotNull(mergeFunction);
    return Collectors.collectingAndThen(
        Collectors.toMap(
            keyFunction, valueFunction, mergeFunction, () -> new TreeMap<K, V>(comparator)),
        ImmutableSortedMap::copyOfSorted);
  }

      Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(
          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction,
          BinaryOperator<V> mergeFunction) {
    throw new UnsupportedOperationException();
  }

  @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0xdecaf;

          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction,
          BinaryOperator<V> mergeFunction) {
    return CollectCollectors.toImmutableMap(keyFunction, valueFunction, mergeFunction);
  }

  /**
   * Returns the empty map. This map behaves and performs comparably to {@link

          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction,
          BinaryOperator<V> mergeFunction) {
    return CollectCollectors.toImmutableMap(keyFunction, valueFunction, mergeFunction);
  }

  /**
   * Returns the empty map. This map behaves and performs comparably to {@link