Error display: errors may be on twice-nested fields

@matthieu @manonbou I came across the following error:

{"batches":{"tasks":{"@id":["task with this urlid already exists."]}},"@context":"https://cdn.happy-dev.fr/owl/hdcontext.jsonld"}

The actual error is serverside, but when it was rendered in the front-end I saw this:

I think this is because the error is nested in batches['tasks']