code: private static void appendModifierKeyword(final StringBuilder buf, final String modifierKeyword) {
          if (buf.length() > 0 && buf.charAt(buf.length() - 1) != ' ') {
              buf.append(' ');
          }
          buf.append(modifierKeyword);
      }
docs: Append a space if necessary (if not at the beginning of the buffer, and the last character is not already a
  space), then append a modifier keyword.
  
  @param buf
  the buf
  @param modifierKeyword
  the modifier keyword