* we're copying into a `contents` array whose type allows it to contain nulls. Still, it's
       * worth noting that we promise not to put nulls into the array in the first `size` elements.
       * We uphold that promise here because our callers promise that `elements` will not contain
       * nulls in its first `n` elements.
       */
      System.arraycopy(elements, 0, contents, size, n);
      size += n;

    int[] expected = {0, 1, 2, 1, 4, 5, 0};
    checkIndexOf(toTest, expected);
  }

  public void testIndexOfImpl_null() {
    List<String> toTest;
    try {
      toTest = createList(String.class, null, "A", "B", null, "C", null);
    } catch (NullPointerException e) {
      // example cannot handle nulls, test invalid
      return;
    }
    int[] expected = {0, 1, 2, 0, 4, 0};
    checkIndexOf(toTest, expected);
  }

   *
   * @throws NullPointerException if any key or value in {@code map} is null
   */
  @SuppressWarnings("unchecked")
  public static <K, V> ImmutableSortedMap<K, V> copyOfSorted(SortedMap<K, ? extends V> map) {
    Comparator<? super K> comparator = map.comparator();
    if (comparator == null) {
      // If map has a null comparator, the keys should have a natural ordering,

    List<@Nullable String> list = newArrayList("a", null, "b", null, "a", null);
    assertEquals(2, Iterators.frequency(list.iterator(), "a"));
    assertEquals(1, Iterators.frequency(list.iterator(), "b"));
    assertEquals(0, Iterators.frequency(list.iterator(), "c"));
    assertEquals(0, Iterators.frequency(list.iterator(), 4.2));
    assertEquals(3, Iterators.frequency(list.iterator(), null));
  }

  @GwtIncompatible // slow (~4s)

                  }
                })
            .named("Sets.filter, no nulls")
            .withFeatures(
                CollectionFeature.SUPPORTS_ADD,
                CollectionFeature.SUPPORTS_REMOVE,
                CollectionFeature.KNOWN_ORDER,
                CollectionSize.ANY,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());
    suite.addTest(

        TreeMultimap.create(StringLength.COMPARATOR, DECREASING_INT_COMPARATOR);
    multimap.put("google", 2);
    multimap.put("google", 6);
    multimap.put(null, 3);
    multimap.put(null, 1);
    multimap.put(null, 7);
    multimap.put("tree", 0);
    multimap.put("tree", null);
    return multimap;
  }

  /** Test that a TreeMultimap created from another uses the natural ordering. */

        current.elemCount = 0;
        // Also clear these fields so that one deleted Entry doesn't retain all elements.
        current.left = null;
        current.right = null;
        current.pred = null;
        current.succ = null;

        current = next;
      }
      successor(header, header);
      rootReference.clear();
    } else {

      cachingHashMap.remove(key);
      return null;
    }
  }

  @CanIgnoreReturnValue
  @Override
  public V put(K key, V value) {
    checkNotNull(key);
    checkNotNull(value);
    Timestamped<V> oldValue = cachingHashMap.put(key, new Timestamped<V>(value, ticker));
    if (oldValue == null) {
      return null;
    }

   * find it when available. When this is null, use the slow way.
   */
  @J2ktIncompatible
  @GwtIncompatible // java.lang.reflect
  @CheckForNull
  private static final Method getStackTraceElementMethod = (jla == null) ? null : getGetMethod();

  /**
   * The "getStackTraceDepth" method, only available on some JDKs so we use reflection to find it
   * when available. When this is null, use the slow way.
   */

   * find it when available. When this is null, use the slow way.
   */
  @J2ktIncompatible
  @GwtIncompatible // java.lang.reflect
  @CheckForNull
  private static final Method getStackTraceElementMethod = (jla == null) ? null : getGetMethod();

  /**
   * The "getStackTraceDepth" method, only available on some JDKs so we use reflection to find it
   * when available. When this is null, use the slow way.
   */