diff --git a/src/Handler/Utils/ExternalExam/Users.hs b/src/Handler/Utils/ExternalExam/Users.hs
index 6c2243cf0..68d6a5875 100644
--- a/src/Handler/Utils/ExternalExam/Users.hs
+++ b/src/Handler/Utils/ExternalExam/Users.hs
@@ -492,7 +492,7 @@ makeExternalExamUsersTable mode (Entity eeId ExternalExam{..}) = do
         
         guessUser' :: ExternalExamUserTableCsv -> DB (Either (NonEmpty (Entity User)) (Entity User))
         guessUser' ExternalExamUserTableCsv{..} = do
-          let criteria = PredDNF $ Set.singleton $ impureNonNull $ Set.fromList $ (PLVariable <$>) $ catMaybes
+          let criteria = PredDNF . maybe Set.empty Set.singleton . fromNullable . Set.fromList . fmap PLVariable $ catMaybes
                 [ GuessUserMatrikelnummer <$> csvEUserMatriculation
                 , GuessUserDisplayName <$> csvEUserName
                 , GuessUserSurname <$> csvEUserSurname