public static <E> Builder<E> builder() {
    return new Builder<>();
  }

  /**
   * Returns a new builder, expecting the specified number of distinct elements to be added.
   *
   * <p>If {@code expectedSize} is exactly the number of distinct elements added to the builder
   * before {@link Builder#build} is called, the builder is likely to perform better than an unsized
   * {@link #builder()} would have.
   *