serialized property
only gets called when the request failed and has to be tried again later
Implementation
Future<Map<String, dynamic>> get serialized async {
//when storing files we have to make sure they are permanently stored, not only in cache
this.multipartFileNames ??= await Future.wait(
_multipartFiles! //either names or files are set
.map((file) async => await OP.permaStoreCachedXFile(
file, LOCALLY_ADDED_PREFIX + file.name)));
return _$RequestDataToJson(this);
}