This way we can find error about not existing batch loader earlier.
Most of the time user will not reuse loaders, as they are quite unique by nature. But if they want to reuse it, they will probably define it in parent serializer, so it should not be a problem
This way we can find error about not existing batch loader earlier. Most of the time user will not reuse loaders, as they are quite unique by nature. But if they want to reuse it, they will probably define it in parent serializer, so it should not be a problem