* boolean)}. If you override {@code headMap(K, boolean)}, you may wish to override {@code
   * headMap} to forward to this implementation.
   */
  protected SortedMap<K, V> standardHeadMap(@ParametricNullness K toKey) {
    return headMap(toKey, false);
  }

  /**
   * A sensible definition of {@link #tailMap(Object)} in terms of {@link #tailMap(Object,

   * boolean)}. If you override {@code headMap(K, boolean)}, you may wish to override {@code
   * headMap} to forward to this implementation.
   */
  protected SortedMap<K, V> standardHeadMap(@ParametricNullness K toKey) {
    return headMap(toKey, false);
  }

  /**
   * A sensible definition of {@link #tailMap(Object)} in terms of {@link #tailMap(Object,