code: private String formatPartialDateToString(final Integer day, final Integer month,
  			final Integer year,
  			final char padding) {
  		if (year == null && month == null && day == null) {
  			return null;
  		}
  
  		if (!isValidYear(year) || !isValidMonth(month) || !isValidDay(day)) {
  			return null;
  		}
  
  		StringBuffer dateString = new StringBuffer(DATE_TOTAL_CHARS);
  
  		append(dateString, year, YEAR_DIGITS, padding);
  		append(dateString, month, MONTH_DIGITS, padding);
  		append(dateString, day, DAY_DIGITS, padding);
  
  		// TRIM trailing spaces (will only "trim" if the padding character is a space)
  		String trimmed = Util.rightTrim(dateString.toString());
  		return trimmed;
  	}
docs: Set the WPartialDateField with the given day, month and year. Each of the day, month and year parameters that
  make up the partial date are optional.
  
  @param day a number from 1 to 31 or null if unknown.
  @param month a number from 1 to 12, or null if unknown.
  @param year a number, or null if unknown.
  @param padding the padding character for the partial date
  @return the formatted partial date, or null if invalid