LDPSerializer should raise `ValidationError` when it receives an invalid urlid
Whilst debugging https://git.startinblox.com/applications/sib-app/issues/493, where a CircleMember is posted with the data 'user': {'@id': 'self'}
, I found that it reaches serializers.py with an empty validated_data
, and responds by creating an empty user: https://git.startinblox.com/djangoldp-packages/djangoldp/blob/master/djangoldp/serializers.py#L632
The serializer should discover that the urlid has been supplied but is not a valid url, and should raise a ValidationError