IsUnique validator recognizes that null always indicates uniqueness.
Justify the use of the Doctrine underscore naming strategy.
Add to value adapter.
Add value validation.
Use IsUnique validator.
Use correct namespace in API Response.
Allow null/empty responses from API.

Return empty body and status 204 for blank responses instead of a
JSON-ified empty string.
Set request object to adapters.
Merge branch 'develop' into feature/installer