JSObject *maybe_headers(JSObject *obj) {
  MOZ_ASSERT(is_instance(obj));
  return JS::GetReservedSlot(obj, Slots::Headers).toObjectOrNull();
}
JSObject *maybe_headers(JSObject *obj) {
  MOZ_ASSERT(is_instance(obj));
  return JS::GetReservedSlot(obj, Slots::Headers).toObjectOrNull();
}