diff --git a/src/main/java/org/gcube/vremanagement/executor/persistence/orientdb/OrientDBPersistenceConnector.java b/src/main/java/org/gcube/vremanagement/executor/persistence/orientdb/OrientDBPersistenceConnector.java
index 6361d9e..320c682 100644
--- a/src/main/java/org/gcube/vremanagement/executor/persistence/orientdb/OrientDBPersistenceConnector.java
+++ b/src/main/java/org/gcube/vremanagement/executor/persistence/orientdb/OrientDBPersistenceConnector.java
@@ -401,8 +401,8 @@ public class OrientDBPersistenceConnector extends
 
 			ODocument doc = getScheduledTaskDocument(db, uuid);
 
-			long timestamp = doc.field(TIMESTAMP);
-			if (timestamp != scheduledTask.getTimestamp()) {
+			Long timestamp = doc.field(TIMESTAMP);
+			if (timestamp!=null && timestamp != scheduledTask.getTimestamp()) {
 				throw new SchedulePersistenceException(
 						"The ScheduledTask has been changed.");
 			}