Fix collections controller 204 (#2740)

The RFC spec for 204s specifies that you can't send through a response
body. The tests didn't pick this up because we're not using a real
webserver during tests.

Fixes #2733

CHANGELOG.md

@@ -36,6 +36,9 @@ and this project adheres to
 
 ### Fixed
 
+- Collections controller sending an invalid response body when a item doesn't
+  exist [#2733](https://github.com/OpenFn/lightning/issues/2733)
+
 ## [v2.10.4] - 2024-11-22
 
 ### Added

lib/lightning_web/controllers/collections_controller.ex

@@ -59,9 +59,7 @@ defmodule LightningWeb.CollectionsController do
          :ok <- authorize(conn, collection) do
       case Collections.get(collection, key) do
         nil ->
-          conn
-          |> put_status(:no_content)
-          |> json(nil)
+          resp(conn, :no_content, "")
 
         item ->
           json(conn, item)

test/lightning_web/collections_controller_test.exs

@@ -131,7 +131,7 @@ defmodule LightningWeb.API.CollectionsControllerTest do
         |> assign_bearer(token)
         |> get(~p"/collections/#{collection.name}/some-unexisting-key")
 
-      assert json_response(conn, 204) == nil
+      assert response(conn, 204) == ""
     end
   end