Do not return prop names when they are not used

lib/plausible/stats/props.ex

@@ -23,10 +23,6 @@ defmodule Plausible.Stats.Props do
         end)
       end
     else
-      query =
-        Plausible.Stats.Query.remove_goal(query)
-        |> Plausible.Stats.Query.put_filter("event:name", nil)
-
       ClickhouseRepo.all(
         from e in base_event_query(site, query),
           inner_lateral_join: meta in fragment("meta as m"),

lib/plausible_web/controllers/api/stats_controller.ex

@@ -508,7 +508,12 @@ defmodule PlausibleWeb.Api.StatsController do
 
     %{"visitors" => %{"value" => total_visitors}} = Stats.aggregate(site, total_q, ["visitors"])
 
-    prop_names = Stats.props(site, query)
+    prop_names =
+      if query.filters["event:goal"] do
+        Stats.props(site, query)
+      else
+        %{}
+      end
 
     conversions =
       Stats.breakdown(site, query, "event:goal", ["visitors", "events"], {100, 1})

test/plausible_web/controllers/api/stats_controller/conversions_test.exs

@@ -37,7 +37,7 @@ defmodule PlausibleWeb.Api.StatsController.ConversionsTest do
                  "name" => "Signup",
                  "count" => 2,
                  "total_count" => 3,
-                 "prop_names" => ["variant"],
+                 "prop_names" => nil,
                  "conversion_rate" => 50
                },
                %{