Object[] hashTableAndSizeAndDuplicate = (Object[]) hashTablePlus;
      Builder.DuplicateKey duplicateKey = (Builder.DuplicateKey) hashTableAndSizeAndDuplicate[2];
      if (builder == null) {
        throw duplicateKey.exception();
      }
      builder.duplicateKey = duplicateKey;
      hashTable = hashTableAndSizeAndDuplicate[0];
      n = (Integer) hashTableAndSizeAndDuplicate[1];

    /**
     * If non-null, a duplicate key we found in a previous buildKeepingLast() or buildOrThrow()
     * call. A later buildOrThrow() can simply report this duplicate immediately.
     */
    @Nullable DuplicateKey duplicateKey;

    /**
     * Creates a new builder. The returned builder is equivalent to the builder generated by {@link
     * ImmutableMap#builder}.
     */
    public Builder() {