code: public DateTimeFormatterBuilder padNext(int padWidth, char padChar) {
          if (padWidth < 1) {
              throw new IllegalArgumentException("The pad width must be at least one but was " + padWidth);
          }
          active.padNextWidth = padWidth;
          active.padNextChar = padChar;
          active.valueParserIndex = -1;
          return this;
      }
docs: Causes the next added printer/parser to pad to a fixed width.
  <p>
  This padding is intended for padding other than zero-padding.
  Zero-padding should be achieved using the appendValue methods.
  <p>
  During formatting, the decorated element will be output and then padded
  to the specified width. An exception will be thrown during printing if
  the pad width is exceeded.
  <p>
  During parsing, the padding and decorated element are parsed.
  If parsing is lenient, then the pad width is treated as a maximum.
  If parsing is case insensitive, then the pad character is matched ignoring case.
  The padding is parsed greedily. Thus, if the decorated element starts with
  the pad character, it will not be parsed.
  
  @param padWidth  the pad width, 1 or greater
  @param padChar  the pad character
  @return this, for chaining, not null
  @throws IllegalArgumentException if pad width is too small