GraphQL API returns types for profile that violate schema

Problem/Motivation

The producer returned a field item for empty fields which could cause
non-nullable sub-fields to return NULL instead (e.g. for a formatted
text field). Returning NULL for an empty field ensures that we don't try
to access sub-fields.

Our profile field isn't allowed to return NULL because all users should
have a profile (and profiles aren't accessible as standalone data) so if
a user is not allowed to view profile data then we just fake this by
returning an empty profile instead. The profile fields are already
nullable because users can choose visibility on a per-field basis.

Steps to reproduce

Proposed resolution

Change the relevant dataproducers.

Remaining tasks

User interface changes

API changes

Data model changes