import: update csv with country

lib/mv/membership/import/member_csv.ex

@@ -549,9 +549,12 @@ defmodule Mv.Membership.Import.MemberCSV do
          line_number,
          actor
        ) do
+    # Convert empty strings to nil for date fields so Ash accepts them
+    member_attrs = sanitize_date_fields(trimmed_member_attrs)
+
     # Create member with custom field values
     member_attrs_with_cf =
-      trimmed_member_attrs
+      member_attrs
       |> Map.put(:custom_field_values, custom_field_values)
 
     # Only include custom_field_values if not empty
@@ -793,6 +796,23 @@ defmodule Mv.Membership.Import.MemberCSV do
     end)
   end
 
+  # Converts empty strings to nil for date fields so Ash can accept them
+  @date_fields [:join_date, :exit_date, :membership_fee_start_date]
+
+  defp sanitize_date_fields(attrs) when is_map(attrs) do
+    Enum.reduce(@date_fields, attrs, fn field, acc ->
+      put_date_field(acc, field, Map.get(acc, field))
+    end)
+  end
+
+  defp put_date_field(acc, field, ""), do: Map.put(acc, field, nil)
+
+  defp put_date_field(acc, field, val) when is_binary(val) do
+    if String.trim(val) == "", do: Map.put(acc, field, nil), else: acc
+  end
+
+  defp put_date_field(acc, _field, _), do: acc
+
   # Formats Ash errors into MemberCSV.Error structs
   defp format_ash_error(%Ash.Error.Invalid{errors: errors}, line_number, email) do
     # Try to find email-related errors first (for better error messages)