[Bug #663] Fix bug

It was always retrieving end data for AggregateOfResourceAllocations
and that's illegal when the aggregate is empty.

FEA: ItEr61S05BugFixing

navalplanner-business/src/main/java/org/navalplanner/business/planner/entities/AggregateOfResourceAllocations.java

@@ -103,6 +103,13 @@ public class AggregateOfResourceAllocations {
         return end != null ? end.getDate() : null;
     }
 
+    /**
+     * Calculates the latest end of all the allocations of this aggregate
+     *
+     * @return
+     * @throws IllegalStateException
+     *             if the aggregate is empty
+     */
     public IntraDayDate getEnd() {
         if (isEmpty()) {
             throw new IllegalStateException("the aggregate is empty");

navalplanner-webapp/src/main/java/org/navalplanner/web/planner/allocation/AllocationResult.java

@@ -103,7 +103,7 @@ public class AllocationResult {
         this.aggregate = aggregate;
         this.daysDuration = aggregate.isEmpty() ? task.getDaysDuration()
                 : aggregate.getDaysDuration();
-        this.end = aggregate.getEnd();
+        this.end = aggregate.isEmpty() ? null : aggregate.getEnd();
         this.newAllocations = newAllocations;
         this.modified = modified;
     }