return sortedMap().ceilingKey(key);
    }

    @Override
    public @Nullable Entry<K, Collection<V>> higherEntry(@ParametricNullness K key) {
      Entry<K, Collection<V>> entry = sortedMap().higherEntry(key);
      return (entry == null) ? null : wrapEntry(entry);
    }

    @Override
    public @Nullable K higherKey(@ParametricNullness K key) {

      return transformEntries(fromMap().headMap(toKey, inclusive), transformer);
    }

    @Override
    public @Nullable Entry<K, V2> higherEntry(@ParametricNullness K key) {
      return transformEntry(fromMap().higherEntry(key));
    }

    @Override
    public @Nullable K higherKey(@ParametricNullness K key) {
      return fromMap().higherKey(key);
    }

    @Override

      return transformEntries(fromMap().headMap(toKey, inclusive), transformer);
    }

    @Override
    public @Nullable Entry<K, V2> higherEntry(@ParametricNullness K key) {
      return transformEntry(fromMap().higherEntry(key));
    }

    @Override
    public @Nullable K higherKey(@ParametricNullness K key) {
      return fromMap().higherKey(key);
    }

    @Override

    assertEquals("three", map.higherKey("r"));
    assertEquals("three", map.ceilingKey("r"));
    assertEquals("one", map.ceilingKey("one"));
    assertEquals(mapEntry("three", 5), map.higherEntry("one"));
    assertEquals(mapEntry("one", 3), map.ceilingEntry("one"));
    assertEquals("one", map.lowerKey("three"));
    assertEquals("one", map.lowerKey("r"));
    assertEquals("one", map.floorKey("r"));

    return keyOrNull(ceilingEntry(key));
  }

  @Override
  public @Nullable Entry<K, V> higherEntry(K key) {
    return tailMap(key, false).firstEntry();
  }

  @Override
  public @Nullable K higherKey(K key) {
    return keyOrNull(higherEntry(key));
  }

  @Override
  public @Nullable Entry<K, V> firstEntry() {