Java奇怪的日期转换异常

private static Date getFormatTime(Date datetime, int addAays, int addMinute) {

		Calendar d = Calendar.getInstance();

		d.add(Calendar.DAY_OF_MONTH, addAays);

		d.add(Calendar.MINUTE, addMinute);

		String dtText = sd.format(d.getTime()) + " " + st.format(datetime.getTime());

		try {

			return sdf.parse(dtText);

		} catch (Exception e) {

			logger.error("日期转换出错."+dtText, e);

		}

		return null;

	}

08:52:57,100 ERROR UserRecProb - 日期转换出错. 2016-12-25 00:00:00

java.lang.NumberFormatException: For input string: ""

	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)

	at java.lang.Long.parseLong(Long.java:453)

	at java.lang.Long.parseLong(Long.java:483)

	at java.text.DigitList.getLong(DigitList.java:194)

	at java.text.DecimalFormat.parse(DecimalFormat.java:1316)

	at java.text.SimpleDateFormat.subParse(SimpleDateFormat.java:1793)

	at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1455)

	at java.text.DateFormat.parse(DateFormat.java:355)

	at com.xfp.message.server.utils.UserRecProb.getFormatTime(UserRecProb.java:27)

	at com.xfp.message.server.utils.UserRecProb.checkUserHavRecPorb(UserRecProb.java:53)