Set<String> listLinks = new HashSet<>(Arrays.asList(list));
            int firstSep = link.indexOf('/');
            if ( firstSep == link.length() - 1 ) {
                // single level
                assertTrue("Link not found " + link, listLinks.contains(link));
            }
            else {
                link = link.substring(0, firstSep + 1);
                // single level

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

  @CollectionSize.Require(ZERO)
  public void testEmptyMapLast() {
    assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

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

  @CollectionSize.Require(ONE)

  @Override
  @CheckForNull
  public Comparator<? super K> comparator() {
    return delegate().comparator();
  }

  @Override
  @ParametricNullness
  public K firstKey() {
    return delegate().firstKey();
  }

  @Override
  public SortedMap<K, V> headMap(@ParametricNullness K toKey) {
    return delegate().headMap(toKey);
  }

  @Override
  @ParametricNullness
  public K lastKey() {

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

  @CollectionSize.Require(ZERO)
  public void testEmptyMapLast() {
    assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

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

  @CollectionSize.Require(ONE)

  @Override
  @CheckForNull
  public Comparator<? super K> comparator() {
    return delegate().comparator();
  }

  @Override
  @ParametricNullness
  public K firstKey() {
    return delegate().firstKey();
  }

  @Override
  public SortedMap<K, V> headMap(@ParametricNullness K toKey) {
    return delegate().headMap(toKey);
  }

  @Override
  @ParametricNullness
  public K lastKey() {

    public Comparator<? super K> comparator() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().comparator();
    }

    @Override
    public K firstKey() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().firstKey();
    }

    @Override
    public K lastKey() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().lastKey();
    }

        delegate().clear();
      }
    };
  }

  @Override
  public @Nullable Entry<K, V> firstEntry() {
    return delegate.firstEntry();
  }

  @Override
  public K firstKey() {
    return delegate.firstKey();
  }

  @Override
  public @Nullable Entry<K, V> floorEntry(K key) {
    return delegate.floorEntry(checkValid(key));
  }

  @Override
  public @Nullable K floorKey(K key) {

  }

  @Override
  @CheckForNull
  public Entry<K, V> pollLastEntry() {
    return Iterators.pollNext(descendingEntryIterator());
  }

  @Override
  @ParametricNullness
  public K firstKey() {
    Entry<K, V> entry = firstEntry();
    if (entry == null) {
      throw new NoSuchElementException();
    } else {
      return entry.getKey();
    }
  }

  @Override
  @ParametricNullness

        delegate().clear();
      }
    };
  }

  @Override
  public @Nullable Entry<K, V> firstEntry() {
    return delegate.firstEntry();
  }

  @Override
  public K firstKey() {
    return delegate.firstKey();
  }

  @Override
  public @Nullable Entry<K, V> floorEntry(K key) {
    return delegate.floorEntry(checkValid(key));
  }

  @Override
  public @Nullable K floorKey(K key) {

      return new TreeRow(rowKey, fromKey, upperBound);
    }

    @Override
    public C firstKey() {
      updateBackingRowMapField();
      if (backingRowMap == null) {
        throw new NoSuchElementException();
      }
      return ((SortedMap<C, V>) backingRowMap).firstKey();
    }

    @Override
    public C lastKey() {
      updateBackingRowMapField();