diff --git a/navalplanner-webapp/src/main/java/org/navalplanner/web/resourceload/LoadPeriodGenerator.java b/navalplanner-webapp/src/main/java/org/navalplanner/web/resourceload/LoadPeriodGenerator.java
index e5dd41e33..fc065d2d2 100644
--- a/navalplanner-webapp/src/main/java/org/navalplanner/web/resourceload/LoadPeriodGenerator.java
+++ b/navalplanner-webapp/src/main/java/org/navalplanner/web/resourceload/LoadPeriodGenerator.java
@@ -91,6 +91,9 @@ abstract class LoadPeriodGenerator {
 
     protected LoadPeriodGenerator(LocalDate start,
             LocalDate end, List<ResourceAllocation<?>> allocationsOnInterval) {
+        Validate.notNull(start);
+        Validate.notNull(end);
+        Validate.notNull(allocationsOnInterval);
         this.start = start;
         this.end = end;
         this.allocationsOnInterval = allocationsOnInterval;