Custom Attributes allow None values #52
Description
It seems like custom_attributes allow for None values.
The documentation says the entries are validated:
https://developer.ftrack.com/api-clients/examples/custom-attribute/index.html#validation
Could you please clarify in the documentation whether None values are allowed? Or is this a bug that should be fixed?
Side note: The ServerError is also a IntegrityError and not ValidationError, but that doesn't really matter for the python wrapper.