Statistics tests: strict first_join_year nil, fee_type_id in URL

test/mv/statistics_test.exs

@@ -46,9 +46,9 @@ defmodule Mv.StatisticsTest do
     end
 
     test "returns nil when no members exist", %{actor: actor} do
-      # Relies on empty member table for this test; may be nil if other tests created members
+      # Expects empty member table (sandbox isolation). If flaky, ensure no other test creates members.
       result = Statistics.first_join_year(actor: actor)
-      assert result == nil or is_integer(result)
+      assert result == nil
     end
   end