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

  @GwtIncompatible // slow (~4s)

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

  @GwtIncompatible // slow (~4s)

      synchronized (mutex) {
        Collection<V> collection = super.get(key);
        return (collection == null) ? null : typePreservingCollection(collection, mutex);
      }
    }

    @Override
    public Set<Map.Entry<K, Collection<V>>> entrySet() {
      synchronized (mutex) {
        if (asMapEntrySet == null) {
          asMapEntrySet = new SynchronizedAsMapEntries<>(delegate().entrySet(), mutex);
        }

      synchronized (mutex) {
        Collection<V> collection = super.get(key);
        return (collection == null) ? null : typePreservingCollection(collection, mutex);
      }
    }

    @Override
    public Set<Map.Entry<K, Collection<V>>> entrySet() {
      synchronized (mutex) {
        if (asMapEntrySet == null) {
          asMapEntrySet = new SynchronizedAsMapEntries<>(delegate().entrySet(), mutex);
        }

//
// Any NULL and non-NULL value combinations for (`run_options`,
// `run_metadata`) are valid.
//
//    - `run_options` may be NULL, in which case it will be ignored; or
//      non-NULL, in which case it must point to a `TF_Buffer` containing the
//      serialized representation of a `RunOptions` protocol buffer.
//    - `run_metadata` may be NULL, in which case it will be ignored; or

    @CheckForNull
    private Iterator<? extends Iterator<? extends T>> getTopMetaIterator() {
      while (topMetaIterator == null || !topMetaIterator.hasNext()) {
        if (metaIterators != null && !metaIterators.isEmpty()) {
          topMetaIterator = metaIterators.removeFirst();
        } else {
          return null;
        }
      }

   * removal operations, and these are reflected in the underlying map.
   *
   * <p>It's acceptable for the underlying map to contain null keys, and even null values provided
   * that the function is capable of accepting null input. The transformed map might contain null
   * values, if the function sometimes gives a null result.
   *
   * <p>The returned map is not thread-safe or serializable, even if the underlying map is.
   *

   * removal operations, and these are reflected in the underlying map.
   *
   * <p>It's acceptable for the underlying map to contain null keys, and even null values provided
   * that the function is capable of accepting null input. The transformed map might contain null
   * values, if the function sometimes gives a null result.
   *
   * <p>The returned map is not thread-safe or serializable, even if the underlying map is.
   *

- Fix availability set cache in vmss cache ([#100110](https://github.com/kubernetes/kubernetes/pull/100110), [@CecileRobertMichon](https://github.com/CecileRobertMichon)) [SIG Cloud Provider]
- Fix how nulls are handled in array and objects in [json patches](https://github.com/evanphx/json-patch). ([#102467](https://github.com/kubernetes/kubernetes/pull/102467), [@pacoxu](https://github.com/pacoxu))

Note that objects with `null` versions, i.e. objects created prior to enabling versioning break the immutability guarantees provided by versioning. When existing object replication is enabled, these objects will be replicated as `null` versions to the remote targets provided they are not present on the target or if `null` version of object on source is newer than the `null` version of object on target.