Build strategy leads to errors

[tbrlpld]

When ever I try to use the "build" strategy with page models and try to validate the model (with full_clean) I get the following error:

django.core.exceptions.ValidationError: {'path': ['This field cannot be blank.'], 'depth': ['This field cannot be null.']}

I guess these must be set by Wagtail in the admin form or during save? It's weird that we cannot build a valid page object without saving it.