diff --git a/src/main/java/org/gcube/data/access/storagehub/AuthorizationChecker.java b/src/main/java/org/gcube/data/access/storagehub/AuthorizationChecker.java
index 2feac3e..4daa523 100644
--- a/src/main/java/org/gcube/data/access/storagehub/AuthorizationChecker.java
+++ b/src/main/java/org/gcube/data/access/storagehub/AuthorizationChecker.java
@@ -48,6 +48,7 @@ public class AuthorizationChecker {
 			Authorizable UserAuthorizable = ((JackrabbitSession) session).getUserManager().getAuthorizable(login);
 			for (AccessControlEntry entry: entries) {
 				Authorizable authorizable = ((JackrabbitSession) session).getUserManager().getAuthorizable(entry.getPrincipal());
+				//TODO; check why sometimes the next line gets a nullpointer
 				if (!authorizable.isGroup() && entry.getPrincipal().getName().equals(login)) return;
 				if (authorizable.isGroup() && ((Group) authorizable).isMember(UserAuthorizable)) return;
 			}