code: public DateTimeFormatterBuilder append(DateTimeFormatter formatter) {
          Jdk8Methods.requireNonNull(formatter, "formatter");
          appendInternal(formatter.toPrinterParser(false));
          return this;
      }
docs: Appends all the elements of a formatter to the builder.
  <p>
  This method has the same effect as appending each of the constituent
  parts of the formatter directly to this builder.
  
  @param formatter  the formatter to add, not null
  @return this, for chaining, not null