* null} even for a map which supposedly does not contain null elements, if the key is not present
   * when {@code getValue()} is called.
   */
  private final class EntryForKey extends AbstractMapEntry<K, V> {
    @ParametricNullness final K key;
    int index;

    EntryForKey(int index) {
      // The cast is safe because we call forEntry only for indexes that contain entries.

    ImmutableListMultimap.Builder<String, Integer> builder = new Builder<>();
    StringHolder holder = new StringHolder();
    holder.string = "one";
    Entry<String, Integer> entry =
        new AbstractMapEntry<String, Integer>() {
          @Override
          public String getKey() {
            return holder.string;
          }

          @Override
          public Integer getValue() {

    }

    @Override
    public boolean isEmpty() {
      return keyIndex.isEmpty();
    }

    Entry<K, V> getEntry(int index) {
      checkElementIndex(index, size());
      return new AbstractMapEntry<K, V>() {
        @Override
        public K getKey() {
          return ArrayMap.this.getKey(index);
        }

        @Override
        @ParametricNullness
        public V getValue() {

   */
  static <K extends @Nullable Object, V extends @Nullable Object> Entry<K, V> unmodifiableEntry(
      Entry<? extends K, ? extends V> entry) {
    checkNotNull(entry);
    return new AbstractMapEntry<K, V>() {
      @Override
      @ParametricNullness
      public K getKey() {
        return entry.getKey();
      }

      @Override
      @ParametricNullness