* @since 10.0
   */
  public MapSplitter withKeyValueSeparator(String separator) {
    return withKeyValueSeparator(on(separator));
  }

  /**
   * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
   * into keys and values using the specified separator.
   *
   * @since 14.0
   */
  public MapSplitter withKeyValueSeparator(char separator) {

  }

  public void testMapSplitter_emptySeparator() {
    assertThrows(IllegalArgumentException.class, () -> COMMA_SPLITTER.withKeyValueSeparator(""));
  }

  public void testMapSplitter_malformedEntry() {
    assertThrows(
        IllegalArgumentException.class,
        () -> COMMA_SPLITTER.withKeyValueSeparator("=").split("a=1,b,c=2"));
  }

  /**

   * @since 10.0
   */
  public MapSplitter withKeyValueSeparator(String separator) {
    return withKeyValueSeparator(on(separator));
  }

  /**
   * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
   * into keys and values using the specified separator.
   *
   * @since 14.0
   */
  public MapSplitter withKeyValueSeparator(char separator) {

    Joiner j = Joiner.on("x").useForNull("y");
    assertThrows(UnsupportedOperationException.class, () -> j.useForNull("y"));
  }

  public void testMap() {
    MapJoiner j = Joiner.on(';').withKeyValueSeparator(':');
    assertThat(j.join(ImmutableMap.of())).isEqualTo("");
    assertThat(j.join(ImmutableMap.of("", ""))).isEqualTo(":");

    Map<@Nullable String, @Nullable String> mapWithNulls = new LinkedHashMap<>();

   *
   * @since 20.0
   */
  public MapJoiner withKeyValueSeparator(char keyValueSeparator) {
    return withKeyValueSeparator(String.valueOf(keyValueSeparator));
  }

  /**
   * Returns a {@code MapJoiner} using the given key-value separator, and the same configuration as
   * this {@code Joiner} otherwise.
   */
  public MapJoiner withKeyValueSeparator(String keyValueSeparator) {

   *
   * @since 20.0
   */
  public MapJoiner withKeyValueSeparator(char keyValueSeparator) {
    return withKeyValueSeparator(String.valueOf(keyValueSeparator));
  }

  /**
   * Returns a {@code MapJoiner} using the given key-value separator, and the same configuration as
   * this {@code Joiner} otherwise.
   */
  public MapJoiner withKeyValueSeparator(String keyValueSeparator) {

    if (h == 0) {
      h = hash(type, subtype, parametersAsMap());
      hashCode = h;
    }
    return h;
  }

  private static final MapJoiner PARAMETER_JOINER = Joiner.on("; ").withKeyValueSeparator("=");

  /**
   * Returns the string representation of this media type in the format described in <a
   * href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>.
   */
  @Override