* #entrySet}. If you override {@code entrySet}, you may wish to override {@code firstEntry} to
   * forward to this implementation.
   */
  protected @Nullable Entry<K, V> standardFirstEntry() {
    return Iterables.<@Nullable Entry<K, V>>getFirst(entrySet(), null);
  }

  /**
   * A sensible definition of {@link #firstKey} in terms of {@code firstEntry}. If you override

   * #entrySet}. If you override {@code entrySet}, you may wish to override {@code firstEntry} to
   * forward to this implementation.
   */
  protected @Nullable Entry<K, V> standardFirstEntry() {
    return Iterables.<@Nullable Entry<K, V>>getFirst(entrySet(), null);
  }

  /**
   * A sensible definition of {@link #firstKey} in terms of {@code firstEntry}. If you override