/**
   * A sensible definition of {@link #firstEntry()} in terms of {@code entrySet().iterator()}.
   *
   * <p>If you override {@link #entrySet()}, you may wish to override {@link #firstEntry()} to
   * forward to this implementation.
   */
  @CheckForNull
  protected Entry<E> standardFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }

  /**
   * A sensible definition of {@link #firstEntry()} in terms of {@code entrySet().iterator()}.
   *
   * <p>If you override {@link #entrySet()}, you may wish to override {@link #firstEntry()} to
   * forward to this implementation.
   */
  @CheckForNull
  protected Entry<E> standardFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }

  /**
   * A sensible definition of {@link #firstEntry()} in terms of {@code entrySet().iterator()}.
   *
   * <p>If you override {@link #entrySet()}, you may wish to override {@link #firstEntry()} to
   * forward to this implementation.
   */
  @CheckForNull
  protected Entry<E> standardFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }