From 323d423fc6d2be0220f09e702eb9a9b4ccc5c3d5 Mon Sep 17 00:00:00 2001
From: Sarah Vaupel <vaupel@cip.ifi.lmu.de>
Date: Mon, 17 Aug 2020 11:08:24 +0200
Subject: [PATCH] Apply 1 suggestion(s) to 1 file(s)

---
 src/Handler/Exam/Users.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Handler/Exam/Users.hs b/src/Handler/Exam/Users.hs
index 1912abbd0..9fcf76c04 100644
--- a/src/Handler/Exam/Users.hs
+++ b/src/Handler/Exam/Users.hs
@@ -973,7 +973,7 @@ postEUsersR tid ssh csh examn = do
 
               guessUser' :: ExamUserTableCsv -> DB (Bool, UserId)
               guessUser' ExamUserTableCsv{..} = 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