code: public PeriodFormatterBuilder appendSeparatorIfFieldsBefore(String text) {
          return appendSeparator(text, text, null, true, false);
      }
docs: Append a separator, which is output only if fields are printed before the separator.
  <p>
  For example,
  <code>builder.appendDays().appendSeparatorIfFieldsBefore(",").appendHours()</code>
  will only output the comma if the days fields is output.
  <p>
  The text will be parsed case-insensitively.
  <p>
  Note: appending a separator discontinues any further work on the latest
  appended field.
  
  @param text  the text to use as a separator
  @return this PeriodFormatterBuilder
  @throws IllegalStateException if this separator follows a previous one