/**
   * Returns the single element contained in {@code iterator}.
   *
   * @throws NoSuchElementException if the iterator is empty
   * @throws IllegalArgumentException if the iterator contains multiple elements. The state of the
   *     iterator is unspecified.
   */
  @ParametricNullness
  public static <T extends @Nullable Object> T getOnlyElement(Iterator<T> iterator) {
    T first = iterator.next();
    if (!iterator.hasNext()) {

  /**
   * Returns the single element contained in {@code iterator}.
   *
   * @throws NoSuchElementException if the iterator is empty
   * @throws IllegalArgumentException if the iterator contains multiple elements. The state of the
   *     iterator is unspecified.
   */
  @ParametricNullness
  public static <T extends @Nullable Object> T getOnlyElement(Iterator<T> iterator) {
    T first = iterator.next();
    if (!iterator.hasNext()) {