}

  public void testGetOnlyElement_withDefault_empty() {
    Iterator<String> iterator = emptyIterator();
    assertEquals("bar", getOnlyElement(iterator, "bar"));
  }

  public void testGetOnlyElement_withDefault_empty_null() {
    Iterator<String> iterator = emptyIterator();
    assertNull(Iterators.<@Nullable String>getOnlyElement(iterator, null));
  }

  }

  public void testGetOnlyElement_withDefault_empty() {
    Iterator<String> iterator = emptyIterator();
    assertEquals("bar", getOnlyElement(iterator, "bar"));
  }

  public void testGetOnlyElement_withDefault_empty_null() {
    Iterator<String> iterator = emptyIterator();
    assertNull(Iterators.<@Nullable String>getOnlyElement(iterator, null));
  }

  /**
   * Returns the empty iterator.
   *
   * <p>The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
   */
  static <T extends @Nullable Object> UnmodifiableIterator<T> emptyIterator() {
    return emptyListIterator();
  }

  /**
   * Returns the empty iterator.
   *
   * <p>The {@link Iterable} equivalent of this method is {@link ImmutableSet#of()}.
   */