CSV export: robust apply_export_filters, single custom_field_ids_union, string boolean_filters, more tests

lib/mv/membership/member_export.ex

@@ -388,20 +388,25 @@ defmodule Mv.Membership.MemberExport do
   - `opts` - Map with `:selected_ids`, `:cycle_status_filter`, `:show_current_cycle`, `:boolean_filters`.
   - `custom_fields_by_id` - Map of custom field id => custom field struct (for boolean filter resolution).
 
-  When `opts.selected_ids` is not empty, returns `members` unchanged. Otherwise applies
-  cycle status filter and boolean custom field filters.
+  When `opts.selected_ids` is not empty, returns `members` unchanged (selected_ids
+  override filters). Otherwise applies cycle status filter and boolean custom field filters.
+
+  Uses `Map.get(opts, :selected_ids, [])` so that `nil` or a missing key is treated as
+  "export all" and filters are applied.
   """
   @spec apply_export_filters([struct()], map(), map()) :: [struct()]
   def apply_export_filters(members, opts, custom_fields_by_id) do
-    if opts[:selected_ids] != [] do
-      members
-    else
+    selected_ids = Map.get(opts, :selected_ids, [])
+
+    if Enum.empty?(selected_ids) do
       members
       |> apply_cycle_status_filter(opts[:cycle_status_filter], opts[:show_current_cycle])
       |> Index.apply_boolean_custom_field_filters(
         Map.get(opts, :boolean_filters, %{}),
         Map.values(custom_fields_by_id)
       )
+    else
+      members
     end
   end