From 9c928b0375c1aab0c46768101849ce8daeae9b81 Mon Sep 17 00:00:00 2001
From: Wolfgang Witt <Wolfgang.Witt@campus.lmu.de>
Date: Mon, 1 Mar 2021 19:39:34 +0100
Subject: [PATCH] fix: make sure to report NoUsers, regardless of rule

---
 src/Handler/Utils/Exam.hs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Handler/Utils/Exam.hs b/src/Handler/Utils/Exam.hs
index 03296e157..ce751ecaf 100644
--- a/src/Handler/Utils/Exam.hs
+++ b/src/Handler/Utils/Exam.hs
@@ -347,7 +347,8 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
                    ]
                takeEnd n chars = drop (length chars - n) chars
             in Map.mapKeysWith Set.union (takeEnd . F.minimum . Set.map length $ Map.keysSet matrUsers) matrUsers
-      _ -> Map.singleton [] $ Map.keysSet users
+      _ | null users-> Map.empty
+        | otherwise -> Map.singleton [] $ Map.keysSet users
 
     occurrences' :: Map ExamOccurrenceId Natural
     -- ^ reduce room capacity for every pre-assigned user by 1