assertNull(navigableMap.lowerEntry(k0()));
    assertNull(navigableMap.lowerKey(k0()));
    assertNull(navigableMap.floorEntry(k0()));
    assertNull(navigableMap.floorKey(k0()));
    assertNull(navigableMap.ceilingEntry(k0()));
    assertNull(navigableMap.ceilingKey(k0()));
    assertNull(navigableMap.higherEntry(k0()));
    assertNull(navigableMap.higherKey(k0()));
  }

  @CollectionSize.Require(ZERO)

    assertNull(navigableMap.lowerEntry(k0()));
    assertNull(navigableMap.lowerKey(k0()));
    assertNull(navigableMap.floorEntry(k0()));
    assertNull(navigableMap.floorKey(k0()));
    assertNull(navigableMap.ceilingEntry(k0()));
    assertNull(navigableMap.ceilingKey(k0()));
    assertNull(navigableMap.higherEntry(k0()));
    assertNull(navigableMap.higherKey(k0()));
  }

  @CollectionSize.Require(ZERO)

    new ForwardingWrapperTester()
        .testForwarding(
            NavigableMap.class,
            new Function<NavigableMap, NavigableMap>() {
              @Override
              public NavigableMap apply(NavigableMap delegate) {
                return wrap(delegate);
              }
            });
  }

  public void testEquals() {
    NavigableMap<Integer, String> map1 = ImmutableSortedMap.of(1, "one");

     * restriction.
     */
    private final Range<C> restriction;

    private final NavigableMap<Cut<C>, Range<C>> rangesByLowerBound;
    private final NavigableMap<Cut<C>, Range<C>> rangesByUpperBound;

    private SubRangeSetRangesByLowerBound(
        Range<Cut<C>> lowerBoundWindow,
        Range<C> restriction,
        NavigableMap<Cut<C>, Range<C>> rangesByLowerBound) {
      this.lowerBoundWindow = checkNotNull(lowerBoundWindow);

        TestSortedMapGenerator<K, V> delegate, Bound to, Bound from) {
      super(delegate, to, from);
    }

    @Override
    NavigableMap<K, V> createSubMap(SortedMap<K, V> sortedMap, K firstExclusive, K lastExclusive) {
      NavigableMap<K, V> map = (NavigableMap<K, V>) sortedMap;
      if (from == Bound.NO_BOUND && to == Bound.INCLUSIVE) {
        return map.headMap(lastInclusive, true);

@GwtIncompatible
public final class SafeTreeMap<K, V> implements Serializable, NavigableMap<K, V> {
  @SuppressWarnings("unchecked")
  private static final Comparator<Object> NATURAL_ORDER =
      new Comparator<Object>() {
        @Override
        public int compare(Object o1, Object o2) {
          return ((Comparable<Object>) o1).compareTo(o2);
        }
      };

  private final NavigableMap<K, V> delegate;

  public SafeTreeMap() {

@GwtIncompatible
public final class SafeTreeMap<K, V> implements Serializable, NavigableMap<K, V> {
  @SuppressWarnings("unchecked")
  private static final Comparator<Object> NATURAL_ORDER =
      new Comparator<Object>() {
        @Override
        public int compare(Object o1, Object o2) {
          return ((Comparable<Object>) o1).compareTo(o2);
        }
      };

  private final NavigableMap<K, V> delegate;

  public SafeTreeMap() {

  protected SortedMap<String, Integer> makePopulatedMap() {
    NavigableMap<String, Integer> map = new SafeTreeMap<>();
    map.put("one", 1);
    map.put("two", 2);
    map.put("three", 3);
    return SerializableTester.reserialize(map);
  }

  @Override
  protected SortedMap<String, Integer> makeEmptyMap() throws UnsupportedOperationException {
    NavigableMap<String, Integer> map = new SafeTreeMap<>();

    }
  }

  private final class NavigableAsMap extends SortedAsMap implements NavigableMap<K, Collection<V>> {

    NavigableAsMap(NavigableMap<K, Collection<V>> submap) {
      super(submap);
    }

    @Override
    NavigableMap<K, Collection<V>> sortedMap() {
      return (NavigableMap<K, Collection<V>>) super.sortedMap();
    }

    @Override

    assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapFirst() {
    assertEquals(a.getKey(), navigableMap.firstKey());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapLast() {
    assertEquals(a.getKey(), navigableMap.lastKey());
  }

  @CollectionSize.Require(SEVERAL)