Solr DIH: empty child document transformer

I will try to explain myself in as much detail as possible and isolating as much as possible from the context. Shortly, I'm trying to create a `DIH` in order to digest some documents as nested. I mean, I need to digest an `one-to-many` relation and put it as nested documents. My `parents` data is

Child documents are not retrieved after DIH

I will try to explain myself in as much detail as possible and isolating as much as possible from the context. Shortly, I'm trying to create a `DIH` in order to digest some documents as nested. I mean, I need to digest an `one-to-many` relation and put it as nested documents. My `parents` data is