fix: empty row on handler function

Closes https://github.com/PostgREST/postgrest/issues/3126

CHANGELOG.md

@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
   - #3124, Fix table's media type handlers not working for all schemas - @steve-chavez
+  - #3126, Fix empty row on media type handler function - @steve-chavez
 
 ## [12.0.1] - 2023-12-12
 

src/PostgREST/Query/Statements.hs

@@ -157,7 +157,8 @@ preparePlanRows countQuery =
 standardRow :: Bool -> HD.Row ResultSet
 standardRow noLocation =
   RSStandard <$> nullableColumn HD.int8 <*> column HD.int8
-             <*> (if noLocation then pure mempty else fmap splitKeyValue <$> arrayColumn HD.bytea) <*> column HD.bytea
+             <*> (if noLocation then pure mempty else fmap splitKeyValue <$> arrayColumn HD.bytea)
+             <*> (fromMaybe mempty <$> nullableColumn HD.bytea)
              <*> nullableColumn HD.bytea
              <*> nullableColumn HD.text
              <*> nullableColumn HD.int8

test/spec/Feature/Query/CustomMediaSpec.hs

@@ -119,6 +119,13 @@ spec = describe "custom media types" $ do
         , matchHeaders = ["Content-Type" <:> "application/json; charset=utf-8"]
         }
 
+    it "should not fail when the function doesn't return a row" $ do
+      request methodGet "/rpc/get_line?id=777" (acceptHdrs "application/vnd.twkb") ""
+        `shouldRespondWith` ""
+        { matchStatus = 200
+        , matchHeaders = ["Content-Type" <:> "application/vnd.twkb"]
+        }
+
   context "Proc that returns scalar based on a table" $ do
     it "can get an image with Accept: image/png" $ do
       r <- request methodGet "/rpc/ret_image" (acceptHdrs "image/png") ""

test/spec/fixtures/schema.sql

@@ -3517,6 +3517,11 @@ returns setof test.lines as $$
   select * from lines;
 $$ language sql;
 
+create or replace function test.get_line (id int)
+returns "application/vnd.twkb" as $$
+  select extensions.st_astwkb(geom)::"application/vnd.twkb" from lines where id = get_line.id;
+$$ language sql;
+
 create or replace function test.get_shop_bles ()
 returns setof test.shop_bles as $$
   select * from shop_bles;