Return 0 when doing DayOfWeek over empty date (#669)

* Return 0 when doing DoW over nulldate
Issue:101248

* Consider both cases, empty date and null date

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Co-authored-by: tomas-sexenian <tsexenian@genexus.com>
Co-authored-by: Gonzalo <gonzalogallotti@gmail.com>

Author: 3 people

common/src/main/java/com/genexus/CommonUtil.java

@@ -1833,6 +1833,8 @@ public static BigDecimal truncDecimal(BigDecimal num , int decimals)
 
 	public static byte dow(Date date)
 	{
+		if	(date == null || date.equals(nullDate()))
+			return 0;
 		Calendar cal = getCalendar();
 		synchronized (cal)
 		{