code: public final StringBuilder appendTo(StringBuilder builder, Iterator<?> parts) {
      try {
        appendTo((Appendable) builder, parts);
      } catch (IOException impossible) {
        throw new AssertionError(impossible);
      }
      return builder;
    }
docs: Appends the string representation of each of {@code parts}, using the previously configured
  separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
  Iterable)}, except that it does not throw {@link IOException}.
  
  @since 11.0