--- a/src/main/java/org/mpi/openmind/repository/services/AbstractPersistenceService.java	Fri Mar 03 18:59:20 2017 +0100
+++ b/src/main/java/org/mpi/openmind/repository/services/AbstractPersistenceService.java	Fri Jun 16 15:41:39 2017 +0200
@@ -667,13 +667,16 @@
 	 * @throws Exception
 	 */
 	private void refreshRelationTarget(Session session, Relation rel) throws Exception {
-		long targetModifOld = rel.getTargetModif();
+		if(rel.getTargetId() == null){
+			throw new Exception("Refreshing entity " + rel.getSourceId() + ", the system found a relation with empty target.");
+		}
 		StringBuilder sb = new StringBuilder("refreshTarget of " + rel.toString() + " to "+rel.printTarget());
 		List<Entity> entityList = this.getEntities(session, rel.getTargetId(), Node.SYS_STATUS_CURRENT_VERSION, rel.getType(), null, false);
 		if(entityList.isEmpty()){
-			throw new Exception("Saving entity " + rel.getSourceId() + ", the system found a relation without target. " + rel.toString());
+			throw new Exception("Refreshing entity " + rel.getSourceId() + ", the system found a relation without target. " + rel.toString());
 		}
 		Entity target = entityList.get(0);
+		long targetModifOld = rel.getTargetModif();
 		rel.setTarget(target);
 		sb.append(" new "+rel.printTarget());
 		// the refresh is logged only if we detect a difference between the relation and the target entity.
@@ -692,13 +695,16 @@
 	 * @throws Exception
 	 */
 	private void refreshRelationSource(Session session, Relation rel) throws Exception {
-		long sourceModifOld = rel.getSourceModif();
+		if(rel.getSourceId() ==  null){
+			throw new Exception("Refreshing entity " + rel.getTargetId() + ", the system found a relation with emtpy source.");
+		}
 		StringBuilder sb = new StringBuilder("refreshSource of " + rel.toString() + " to "+rel.printSource());
 		List<Entity> entityList = this.getEntities(session, rel.getSourceId(), Node.SYS_STATUS_CURRENT_VERSION, rel.getType(), null, false);
 		if(entityList.isEmpty()){
-			throw new Exception("Saving entity " + rel.getTargetId() + ", the system found a relation without source. " + rel.toString());
+			throw new Exception("Refreshing entity " + rel.getTargetId() + ", the system found a relation without source. " + rel.toString());
 		}
 		Entity source = entityList.get(0);
+		long sourceModifOld = rel.getSourceModif();
 		rel.setSource(source);
 		sb.append(" new "+rel.printSource());
 		// the refresh is logged only if we detect a difference between the relation and the source entity.