[backend] bug fix to resolve nullpointer in constructor

iTrust/src/edu/ncsu/csc/itrust/beans/DiagnosisStatisticsBean.java

@@ -91,9 +91,13 @@ public class DiagnosisStatisticsBean {
 		this.zipStats = zipStats;
 		this.regionStats = regionStats;
 		this.stateStats = stateStats;
-		this.allStats = allStats;
-		this.startDate = (Date) startDate.clone();
-		this.endDate = (Date) endDate.clone();
+        this.allStats = allStats;
+        if (startDate != null) {
+            this.startDate = (Date) startDate.clone();
+        }
+        if (endDate != null) {
+            this.endDate = (Date) endDate.clone();
+        }
 	}
 
 	/**