QPR-12235 only check when not null dates

Author: damienbarker

OREData/ored/portfolio/schedule.cpp

@@ -337,7 +337,8 @@ Schedule makeSchedule(const ScheduleRules& data, const Date& openEndDateReplacem
 
     Date firstDate = parseDate(data.firstDate());
     Date lastDate = parseDate(data.lastDate());
-    QL_REQUIRE(firstDate <= lastDate, "Schedule::makeSchedule firstDate must be before lastDate");
+    if (firstDate != Date() && lastDate != Date())
+        QL_REQUIRE(firstDate <= lastDate, "Schedule::makeSchedule firstDate must be before lastDate");
 
     Period tenor = parsePeriod(data.tenor());