@SuppressWarnings("unchecked")
  static final Comparator<?> NATURAL_ORDER = Ordering.natural();

  // This reference is only used by GWT compiler to infer the keys and values
  // of the map that needs to be serialized.
  private @Nullable Comparator<? super K> unusedComparatorForSerialization;
  private @Nullable K unusedKeyForSerialization;
  private @Nullable V unusedValueForSerialization;

   * com.google.common.io.ByteStreams#newDataOutput()} to get a growable buffer.
   */
  public static byte[] toByteArray(long value) {
    // Note that this code needs to stay compatible with GWT, which has known
    // bugs when narrowing byte casts of long values occur.
    byte[] result = new byte[8];
    for (int i = 7; i >= 0; i--) {
      result[i] = (byte) (value & 0xffL);