Use protolude 0.2.2, replace undefined with witness

protolude provides headMay since 0.2.2, it can be used instead of safe.

src/PostgREST/ApiRequest.hs

@@ -105,7 +105,7 @@ userApiRequest :: Schema -> Request -> RequestBody -> Either ApiRequestError Api
 userApiRequest schema req reqBody
   | isTargetingProc && method `notElem` ["GET", "POST"] = Left ActionInappropriate
   | topLevelRange == emptyRange = Left InvalidRange
-  | shouldParsePayload && isLeft payload = either (Left . InvalidBody . toS) undefined payload
+  | shouldParsePayload && isLeft payload = either (Left . InvalidBody . toS) witness payload
   | otherwise = Right ApiRequest {
       iAction = action
       , iTarget = target

src/PostgREST/App.hs

@@ -61,7 +61,6 @@ import           PostgREST.OpenAPI
 
 import           Data.Function (id)
 import           Protolude              hiding (intercalate, Proxy)
-import           Safe                   (headMay)
 
 postgrest :: AppConfig -> IORef (Maybe DbStructure) -> P.Pool -> IO UTCTime -> IO () -> Application
 postgrest conf refDbStructure pool getTime worker =

src/PostgREST/DbRequestBuilder.hs

@@ -231,7 +231,7 @@ getJoinConditions (Relation Table{tableSchema=tSchema, tableName=tN} cols Table{
      | typ == Many ->
         let ltN = fromMaybe "" (tableName <$> lt) in
         zipWith (toJoinCondition tN ltN) cols (fromMaybe [] lc1) ++ zipWith (toJoinCondition ftN ltN) fcs (fromMaybe [] lc2)
-     | typ == Root -> undefined
+     | typ == Root -> witness
   where
     toJoinCondition :: Text -> Text -> Column -> Column -> JoinCondition
     toJoinCondition tb ftb c fc =

src/PostgREST/QueryBuilder.hs

@@ -207,7 +207,7 @@ pgFmtLit x =
    else slashed
 
 requestToCountQuery :: Schema -> DbRequest -> SqlQuery
-requestToCountQuery _ (DbMutate _) = undefined
+requestToCountQuery _ (DbMutate _) = witness
 requestToCountQuery schema (DbRead (Node (Select{where_=logicForest}, (mainTbl, _, _, _, _)) _)) =
  unwords [
    "SELECT pg_catalog.count(*)",
@@ -272,7 +272,7 @@ requestToQuery schema isParent (DbRead (Node (Select colSelects tbls logicForest
     --the following is just to remove the warning
     --getQueryParts is not total but requestToQuery is called only after addJoinConditions which ensures the only
     --posible relations are Child Parent Many
-    getQueryParts _ _ = undefined
+    getQueryParts _ _ = witness
 requestToQuery schema _ (DbMutate (Insert mainTbl pkCols p@(PayloadJSON _ pType pKeys) onConflct logicForest returnings)) =
   unwords [
     ("WITH " <> ignoredBody) `emptyOnFalse` not payloadIsEmpty,