return new TreeMap<>();
  }

  /**
   * Creates a <i>mutable</i> {@code TreeMap} instance with the same mappings as the specified map
   * and using the same ordering as the specified map.
   *
   * <p><b>Note:</b> if mutability is not required, use {@link
   * ImmutableSortedMap#copyOfSorted(SortedMap)} instead.
   *

    // A few elements.
    a = asList(4, 8, 15, 16, 23, 42);
    b = asList(4, 8, 15, 16, 23, 42);
    assertTrue(Iterators.elementsEqual(a.iterator(), b.iterator()));

    // The same, but with nulls.
    a = Arrays.<@Nullable Integer>asList(4, 8, null, 16, 23, 42);
    b = Arrays.<@Nullable Integer>asList(4, 8, null, 16, 23, 42);
    assertTrue(Iterators.elementsEqual(a.iterator(), b.iterator()));

  /** The HTTP {@code Cache-Control} header field name. */
  public static final String CACHE_CONTROL = "Cache-Control";
  /** The HTTP {@code Content-Length} header field name. */
  public static final String CONTENT_LENGTH = "Content-Length";
  /** The HTTP {@code Content-Type} header field name. */
  public static final String CONTENT_TYPE = "Content-Type";
  /** The HTTP {@code Date} header field name. */
  public static final String DATE = "Date";

  }

  /**
   * Returns an immutable sorted multiset containing the elements of a sorted multiset, sorted by
   * the same {@code Comparator}. That behavior differs from {@link #copyOf(Iterable)}, which always
   * uses the natural ordering of the elements.
   *
   * <p>Despite the method name, this method attempts to avoid actually copying the data when it is