/**
   * The keys of the entries in the map, in the range of [0, size()). The keys in [size(),
   * keys.length) are all {@code null}.
   */
  @VisibleForTesting @CheckForNull transient @Nullable Object[] keys;

  /**
   * The values of the entries in the map, in the range of [0, size()). The values in [size(),
   * values.length) are all {@code null}.
   */