[Bug #816] Fix bug

The problem lied in that the @NotNull annotation was applied to a
field. This is dangerous because if the object that is being validated
is a proxy, the value is always null. Now the annotation was moved to
the getter.

FEA: ItEr69S04BugFixing

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

@@ -443,7 +443,6 @@ public abstract class ResourceAllocation<T extends DayAssignment> extends
     private AssignmentFunction assignmentFunction;
 
     @OnCopy(Strategy.SHARE)
-    @NotNull
     private ResourcesPerDay resourcesPerDay;
 
     private Integer intendedTotalHours;
@@ -1418,6 +1417,7 @@ public abstract class ResourceAllocation<T extends DayAssignment> extends
         return calculateResourcesPerDayFromAssignments(getConsolidatedAssignments());
     }
 
+    @NotNull
     public ResourcesPerDay getResourcesPerDay() {
         if (resourcesPerDay == null) {
             return ResourcesPerDay.amount(0);