Revert "openolat#165: allow the 'latestemailed' column to be set to null as...

Revert "openolat#165: allow the 'latestemailed' column to be set to null as this is done in the migrateInfosNotificationsNotDesired migration (14.2)" as the issue is solved upstream by setting the field in the upgrade process.

This reverts commit aa0f3e46.

src/main/java/org/olat/core/commons/services/notifications/model/SubscriberImpl.java

@@ -100,7 +100,7 @@ public class SubscriberImpl implements Subscriber, CreateInfo, Persistable  {
 	
 	// when the user latest received an email concerning this subscription; may be null if no email has been sent yet
 	@Temporal(TemporalType.TIMESTAMP)
-	@Column(name="latestemailed", nullable=true, insertable=true, updatable=true)
+	@Column(name="latestemailed", nullable=false, insertable=true, updatable=true)
 	private Date latestEmailed; 
 	
 	@Column(name="subenabled", nullable=false, insertable=true, updatable=true)