code: public static CSLDate toDateSingle(String year, String month) {
  		int m = toMonth(month);
  		
  		//parse year
  		int y = -1;
  		Boolean circa = null;
  		if (year != null && year.length() >= 4) {
  			if (StringUtils.isNumeric(year)) {
  				y = Integer.parseInt(year);
  			} else {
  				String fourDigit = year.substring(year.length() - 4);
  				if (StringUtils.isNumeric(fourDigit)) {
  					y = Integer.parseInt(fourDigit);
  					if (year.length() > 4) {
  						circa = Boolean.TRUE;
  					}
  				}
  			}
  		}
  		
  		//create result
  		CSLDateBuilder builder = new CSLDateBuilder();
  		if (y < 0) {
  			return null;
  		}
  		if (m < 0) {
  			return builder.dateParts(y).circa(circa).build();
  		}
  		return builder.dateParts(y, m).circa(circa).build();
  	}
docs: Parses the given year and month to a {@link CSLDate} object. Does not
  handle ranges.
  @param year the year to parse. Should be a four-digit number or a String
  whose last four characters are digits.
  @param month the month to parse. May be a number (<code>1-12</code>),
  a short month name (<code>Jan</code> to <code>Dec</code>), or a
  long month name (<code>January</code> to <code>December</code>). This
  method is also able to recognize month names in several locales.
  @return the {@link CSLDate} object or null if both, the year and the
  month, could not be parsed