@@ -199,7 +199,7 @@ patchThatChangesMap oldByIndex newByIndex = patch
199199 putRemainingKeys $ Set.delete k fromKs
200200 return $ NodeInfo (From_Move k) $ Just undefined -- There's an existing value, and it's here, so no patch necessary
201201 else do
202− (fromK, remainingKeys) <- return . fromJust $ Set.minView fromKs -- There's an existing value, but it's not here; move it here
202+ (fromK, remainingKeys) <- return . fromMaybe (error "patchThatChangesMap: impossible: fromKs was empty") $ Set.minView fromKs -- There's an existing value, but it's not here; move it here
203203 putRemainingKeys remainingKeys
204204 return $ NodeInfo (From_Move fromK) $ Just undefined
205205 Map.traverseWithKey f newByIndex